To find x we are gonna use the cosine formula. 
Cos 0 = adj/hyp 
0 represents theta 
Cos 0 = adj/hyp
Cos 0 = 25/40
Convert 25/40 to decimal from 
25/40 = 0.625 
On a scientific calculator press the key “2nd F” or “Shift” then “cos”(which would give cos inverse) then type 0.625 equal. 
Cos-1 0 0.625
= 51.31 degrees 
x is therefore 51.3 degrees to the nearest tenth