First, we must find angle c:
180 - (73 + 42) = 65 degrees
Then, we use the question fro, the law of sine, which is:
angle A/ side A = angle B/ side B = angle C/ side C
The side this is opposite to the angle, it's the angle that we use. So, opposite to angle C is 28.7 . We have the equation:
65°/28.7 = 73°/a
Cross multiply and divide, and we get a = 32.2
