Step-by-step explanation:
FYT and UYF are supplementary angles (together they cover all angles around Y on one side of the line TU, and that's is in total 180°).
so,
FYT = 180 - 42 1/8 = 137 7/8°
as 180 - 42 = 138, and then we subtract another 1/8. that gives 137 7/8.
