Which paint costs the most per quart?

Glide Paint: 1 gallon for $28.92
Smooth Paint: 3 quarts for $22.75
One-Coat Paint: 4 pints for $15.00

Smooth Paint

Step-by-step explanation:

Glide Paint is the simplest and cheapest: 28.92 per gallon

Smooth Paint is 3 quarts for 22.75. That equates to roughly $7.58333333 per quart. There are 4 quarts in a gallon. So $7.583333333*4 = $30.33 per gallon

One-Coat Paint is 4 pints for $15.00. There are 8 pints in a gallon, so double $15 and you get $30

TL;DR: Glide Paint: $28.92, One-Coat Paint: $30, Smooth Paint: $30.33

a. is correct