#### Answer

a=3

#### Work Step by Step

We first subtract by 2a on both sides to get that $5=7a-16$. We need to get the a alone. Thus, we cancel out the subtraction by adding 16 on both sides. This leaves us with the equation$21=7a$. In order to cancel out multiplication, we use division, so we divide both sides by 7 to get that a=3. We plug 3 in for a and confirm that our answer is, indeed, correct.