Answer:
39°
Step-by-step explanation:
The sum of AXE, AXC and CXF will be 180 because they together span a straight line (EF).
So: y + 90 + y - 12 = 180, which is an equation you can solve by simplifying it:
y + 90 + y - 12 = 180
2y + 78 = 180
y + 39 = 90
y = 90 - 39 = 51
So AXE = 51
AXC = 90
CXF = 51-12 = 39 (the answer)
Check: 51+90+39 = 180
