Use SOHCAHTOA. Since we are looking for the hypotenuse, you must use sine or cosine. Since, we are given the adjacent side, use cosine.
cosx=a/h
cos45=8/h
√2/2=8/h
*Cross multiply*
h√2=16
*Divide both sides by √2*
h=16/√2
*Multiply by √2/√2*
h=(16√2)/2
*Simplify the fraction*
h=8√2
Hope this helps!!