That angle at the top looks like a right angle. If it is, that makes the problem easy.
If it is not a right angle, the problem doesn't provide enough information for me to solve it.
If the angle at the top is in fact 90o then we have a right triangle and can use Pythagoras' Theorem.
Pythagoras' Theorem hypotenuse2 = leg12 + leg22
substitute known values 92 = 42 + (X +2)2
subtract 42 from both sides
and rearrange terms (X + 2)2 = 92 – 42 No real reason to rearrange; I just prefer the unknown on the left.
(X + 2)2 = 81 – 16 = 65
take square root of both sides X + 2 = sqrt(65)
subtract 2 from both sides X = sqrt(65) – 2