One Way: Use FOIL to find your solutions.
b.
(x - 3)(x + 2)
= x² + 2x - 3x - 6
= x² - x - 6
c.
(x + 3)(x - 2)
= x² - 2x + 3x - 6
= x² + x - 6
d.
(x + 5)(x + 1)
= x² + x + 5x + 5
= x² + 6 x + 5
a.
(x +3)(x+2)
= x² + 2x + 3x + 6
= x² + 5x + 6
A. is your solution.