Law of sines and cosines

Question

In Triangle ABC, m<A=30^o , m<B=80^o , a=18in. Find the length of C.

Answer 1

Grace:

m<A + m<B + m<C =180 so that m<C = 70°

Use the law of sines sin(A)/a = sin(C)/c or sin(30)/18 = sin(70)/c

Answer 2