As Celine's age is 28, and is 4 more than Drake, we need to find Drake's age. Therefore, we need to reverse the equation, where d is the answer:
d + 4 = 28
We need to isolate the letter d, so upgrade each side by 4:
d + 4 (-4) = 28(-4)
d = 24
This means Drake's age is 24.