How would i solve this system of equations? 2y+x=-17 5x-4y=-15

On ryan's last social studies test there were two types of questions true/false worth 3 points each and multiple choice questions worth 4 points each

Can someone me immediately, this is due by midnight! if you can't see the question, i'll text it to you. show the steps you took to get your answer.

What is the sum of the measures of the interior angles of an octagon