1.c

// before

void foo() {
  // some code
  bar(); // not yet defined
}

void bar() {
  // some code
  foo();
}

// after

// Do foo things
void foo();
// do bar things
void bar();

void foo() {
  // some code
  bar(); // signature already above, everything fine
}

void bar() {
  // some code
  foo();
}

2.c

// before

void choosePayroll() {
    printf("-----------------------------------------------\n");
    printf("Press '1' to access the Manager's payroll\n");
    printf("Press '2' to access the Hourly worker's payroll\n");
    printf("Press '3' to access Commission worker's payroll\n");
    printf("Press '4' to access Pieceworkers's payroll\n");
    printf("Press 'Q' to access Manager's payroll\n");
    printf("-----------------------------------------------\n");
}

// after

const char* payrollOutput = 
  "-----------------------------------------------\n"
  "Press '1' to access the Manager's payroll\n"
  "Press '2' to access the Hourly worker's payroll\n"
  "Press '3' to access Commission worker's payroll\n"
  "Press '4' to access Pieceworkers's payroll\n"
  "Press 'Q' to access Manager's payroll\n"
  "-----------------------------------------------\n";

// somewhere later in the code
printf(payrollOutput);

3.c

printf("Press 'R' to return back to the main menu\n\n");
printf("Press 'E' to exit to the total\n");
scanf_s(" %c", &charReturn); // space before %c to tell scanf to skip the leading whitespace
switch (charReturn)
{
  // and so on
}

// sanitize the input:

switch(toLower(charReturn))
{
  // and so on
}

4.c

// before
printf("Please enter the quantity of Item 1 produced this week: ");
scanf_s("%f", &quantityItem1);
printf("-----------------------------------------------\n");
printf("Please enter the quantity of Item 2 produced this week: ");
scanf_s("%f", &quantityItem2);

// after

const char* separator = "-----------------------------------------------\n";

// something along these lines, a little rough
float readFloat(char* message){
    float target;
    do{
        printf(message);
    }while(!scanf_s("%f", &target))
    
    return target;
}

quantityItem1 = readFloat("Please enter the quantity of Item 1 produced this week: ");
printf(separator);
quantityItem2 = readFloat("Please enter the quantity of Item 2 produced this week: ");

8and9.pseudo

// very much pseudo code, just to demonstrate the gist

// now
mainMenu()
    case 1: showA()
    case 2: showB()
    case q: quit;
   
float showA()
    someOutput()
    var target = readSomeInputs()
    case r: mainMenu() // recursive
    return target;
    
float showB() // see showA

So what happens to your stack:
User enters: stack = mainMenu
input 1: stack = mainMenu, showA
input r: stack = mainMenu, showA, mainMenu
input 2: stack = mainMenu, showA, mainManu, showB

you get the picture.

The code should rather work like so:

mainMenu()
    case 1: showA(&target)
    case 2: showB()
    case q: quit;
   
void showA(float* target)
    someOutput()
    target = readSomeInputs()
    case r: return
    case e: totalResult()