I need someone to explain how to find the answer

Solve the system of equations. y= 2x y= x^2 - 15

Mr and mrs smith buy tickets for themselves and their four children. the cost of an adult ticket is ? 6 more than the adult ticket. the total cost of the six tickets is ? 40.50 work out the cost of an adult ticket. in your working let c be the cost of the child ticket and a be the cost of the adult ticket.

Find the maximum value of p= 4x + 5y subject to the following constraints :