Hello from MrBillDoesMath!
Answer:
y = 75 degrees
Discussion:
1) The sum of the angles of a convex quadrilateral is 360 degrees
2) Angle G + 80 = 180 (as there are 180 degrees in a line).
Hence G = 180 - 80 = 100
So using 1) and 2) gives
angle G + 120 + 65 + y = 360 => as angle G = 100
100 + 120 + 65 + y = 360 => combine constants
285 + y = 360 => 360 - 285 = 75
y = 75
Thank you,
MrB
