Answer:
b = 4, b = 6
Explanation:
consider the left side
x² + 10x + 24
consider the factors of the constant term (+ 24) which sum to give the coefficient of the x- term (+ 10)
the factors are + 4 and + 6
then
x² + 10x + 24 = (x + 4)(x + 6) = (x + 6)(x + 4)
then (x + b) = (x + 4) or (x + 6)
with b = 4 or b = 6