59 is the sum of 16 and Donnie's saving. Use the variable d to represent Donnie's saving.

59 is the sum of 16 and Donnie's saving. Use the variable d to represent Donnie's saving.

The phrase the sum of means we add Donnie's savings of d to 16:
d + 16

The phrase is means an equation, so we set d + 16 equal to 59
d + 16 = 59 <-- This is our algebraic expression

Now, if the problem asks you to solve for d, then you type the algebraic expression into our search engine to get:
d = 43