Some body help me out??

Can someone explain the elimination method to me for this problem?

Pyotr tchaikovsky sporting goods operates on a 45% overhead based on the selling price, which results in an overhead of $65.34 on the newest version of an air hockey game set. if the air hockey game set costs pyotr tchaikovsky sports $49.32, find the selling price, the markup, and the net profit.

Over which interval is the graph of f(x) = x2 + 5x + 6 increasing?