The two angles form a straight line which is equal to 180 degrees. This makes the angles supplemtary.
To find x, add the two angles together to equal 180:
7x + x+20 = 180
Combine like terms:
8x + 20 = 180
Subtract 20 from both sides:
8x = 160
Divide both sides by 8:
X = 20
That angle would also be 45
Surface Area = 2πr² + 2πrh
Surface Area = 2π(7)² + 2π(7)(15) = 308π in²²
Answer: 308π in²