Exercise 62 Page 320

The first step in simplifying this expression is to identify which, if any, terms can be combined. Remember, only like terms — constant terms or terms with the same variable — can be combined. In this case, we have two $d\text{-terms}$ and one $\text{constant}.$ Only the $d\text{-terms}$ can be combined, so to simplify the expression we will rearrange it according to the Commutative Property of Addition and then combine like terms.