please tell me what x =?

Since this is a right triangle, we can use one of the three main trigonometric functions: sine, cosine, or tangent.
Remember: SOH-CAH-TOA
Looking from angle x, we know the opposite side and the adjacent side. Therefore, we should use the tangent function to solve.
tan(x) = 8/10
x = tan^-1(8/10)
x = 38.7 degrees
Hope this helps!