What is the value of x? a. 56 b. 78 c. 12 d. 24

X = 78, because 
1) The last angle (the one without the X, equals 24 degrees)
2) 180 - 24 = 156
3) 156/2 = x
x = 78

hope this helps

X + x + 24 = 180
2x = 156
  x = 78

answer
B. 78

The answer is part a: use