http://prntscr.com/lfi57v

i know we use tan, but dont know how to solve it

tan= 15/8?

15/8 = 1.875

to find the ANGLE arctan (1.875) arctan is tangent inverse...= 61.92 degrees

Yes tan= 15/8 it's between 61,62 degrees!

tan x = 15 / 8

To find the angle x, take the arctan of 15/8

arctan (15/8) ≈ 61.93°