Solve triangle using law of sine

There are 20 children in the cast of a class play and 8 of the children are boys of the boys 4 have a speaking part in the play and of the girls 8 do not have a speaking part in the play if a child from the cast of the place chosen at random what is the probability that the child has a speaking part

Ineeeeed this is due tomorrow and i dont know the answer can you find all the exponents

What is an alternate exterior angle