Chapter 2 - Solving Equations - 2-2 Solving Two-Step Equations - Practice and Problem-Solving Exercises - Page 91: 20

a=100

We need to get the a alone, so we cancel out the subtraction by adding 18 on both sides. This leaves us with the equation $a/5=20$. We cancel out division using multiplication, so we multiply both sides by 5 to get that a=100. We plug 100 in for a and confirm that our answer is, indeed, correct.