Hi,
Theorem 9.11: Law of Cosines says c^2 = a^2 + b^2 - 2ab cos C
Lets make c^2 = x^2
So, x^2 = 20^2 + 13^2 - 2(20)(13) cos 93˚
x^2 = 400 + 169 - 520 cos 93˚
x^2 = 569 - 520 cos 93˚
x^2 = 49 cos 93˚
√x^2 = 49 cos 93˚
x = 7√cos(93˚)
I was not sure if that is the answer you were looking for but there you have the last side value.
XD