The answer is d. x² + 6x + 8.
Let's go through all examples.
a. x² + 8x + 16 = 0
x² + 2 4 x + 4² = 0
(x + 4)² = 0
x + 4 = 0
x = -4 one solution
b. x² + 7x + 49/4 = 0
x² + 2 7/2 x + (7/2)² = 0
(x + 7/2)² = 0
x + 7/2 = 0
x = -7/2 one solution
c. x² + 10x + 25 = 0
x² + 2 5 x + 5² = 0
(x + 5)² = 0
x + 5 = 0
x = -5 one solution
This leaves choice d as the equation with more than one solution.
