3d trigenomatry , need help , with step by step working please

The angle you want - call it θ - is such that

tan(θ) = FC / AC

Find the length of the diagonal AC, i.e. a diagonal of the rectangle ABCD. ABC forms a right triangle with legs AB = 70 and BC = 50, so

AC² = AB² + BC²

→   AC = √(70² + 50²) = 10 √74

Find FC using the given angle of the sloping face:

tan(30º) = FC / BC

→   1/√3 = FC / 50

→   FC = 50/√3

Now solve for θ :

tan(θ) = (50/√3) / (10 √74)

→   tan(θ) = 5/√222

→   θ ≈ 18.6º

prime

the number 37 is prime