Can someone explain how to do this?

So in a kite the total angles will add up to be 360°
Angles F and H are congruent (they are the same angle) so they will be the same number of °.
The formula we can use to find F and H is:
87+31+2x=360
(F and H are represented by 2x because they are the same angle twice).

Solving formula:

87+31+2x=360
118+2x=360
2x=360-118
2x=242
2x/2=242/2
x=121

So now we know both angle F and H equal 121° Hope this help! Comment if you have anymore questions