The solution set of 5x + 6-24 is the set of all real values of x such that:
A. X <-24
B. x>-6
C. X<-6
D. X > 6
E. X < 6

They gave you a set of numbers that you replace the variable x in the equation to see if it gives a correct answer so just do exactly that.

6 + 2x = 24
6 + 2(6) = 24
6 + 12 = 24
18 = 24 so incorrect. both sides are not equal to each other.

6 + 2x = 24
6 + 2(9) = 24
6 + 18 = 24
24 = 24 so correct. both sides are equal to each other.

6 + 2x = 24
6 + 2(15) = 24
6 + 30 = 24
36 = 24 so incorrect. both sides are not equal to each other.

6 + 2x = 24
6 + 2(16) = 24
6 + 32 = 24
38 = 24 so incorrect. both sides are not equal to each other.

so your answer is b) 9