12.)
x = total number of students
9 leave, which means x - 9
After the nine leave, there are 11 left, which means x - 9 = 11
Solve accordingly, add nine on both sides of the equation to isolate the variable.
x = 20
13.)
Product = multiplication problem, so w * 7 = 42
Solve accordingly, divide both sides of the equation by 7 to isolate the variable. w = 6.
To check your answer, all you have to do is plug in the value you found, if the equation is true, then your answer is correct!
