First we need to simplify the side lengths
Squared root of 21 is 4.58
Squared root of 85 is 9.22
Now the next step is to find the angle of N
We have the opposite and hypotenuse of angle N so we can use Sin
The equation for Sin is : opposite/hypotenuse
Since we are finding an angle we need to use sin of -1
Sin^-1 ( opposite / hypotenuse)
Sin ^1 (4.58/9.22) = about 30 degrees
Because we need to find cos we need the adjacent side length.
We can use the formula a^2 + b^2 = c^2
4.58^2 + b^2 = 9.22^2
B = 8
Plug in 30 degrees for the cos (n)
Cos = adjacent/ hypotenuse
Cos (30) = 8/9.22 = 0.87
Answer is 0.87