Please help with this problem?!

How do you use the elimination method for this question? explain, because i really want to understand!

Which shows the correct solution of the equation 1/2a+2/3b=50, when b=30?

The first side of a triangle measures 5 in less than the second side, the third side is 3 in more than the first side, and the perimeter is 17 in. how long is the third side? if s represents the length of the second side, which of the following represents the length of the third side? s-5 ws-2 s+ 3 next question ask for turn it in