This a pretty typical right triangle trig problem; the first step is to figure out what we have and what we want in relation to an acute angle in the problem.
Here we have a right triangle, G=90°, and we're given angle F=23°. So we have to name everything in relation to F.
31 = FG is adjacent to F.
x = GE is opposite to F.
OK, we have an opposite and adjacent; that tells us we need to use the tangent of F. Let's write it:
tan 23° = tan F = opp/adj = x/31
Solving,
x = 31 tan 23°
I hate the calculator part. I used to love that part.
x = 31 tan 23° ≈ 13.16 feet
Answer: 4) x ≈ 13.2 ft