Hello from MrBillDoesMath!
Answer:
4
Discussion:
As vertical angles are equal, Angle 3 = Angle 2, so
Angle 3 = 3x + 2 (A)
Angles 3 and 7 are corresponding angles and hence equal. So
Angle 3 = Angle 7 => use (A) above and Angle 7 = x + 10
3x + 2 = x + 10 => subtract x from both sides
3x -x + 2 = x - x + 10 =>
2x + 2 = 10 => subtract 2 from both sides
2x = 10 -2 = 8
x = 8/2 = 4
which is the first choice
Thank you,
MrB