A. first total salary (S) is what is being found so put that on one side of the equal side, then 100 dollars are being made and this is not changed so we don't need a variable, put that on the other side of the equal sign. and since sales (X) is changing, keep the variable, 30% of that is added to the salary, so multiply that by x (first turn it into a decimal, divide it by 100) and add that to the initial 100
S=100+.3X
B. do the same thing above but with a new decimal and initial salary
S=150+.15X
C. since they both need to be equal (S=S) you can replace the S on one equation with the other
100+.3X=150+.15X