What do i put for the sequences?

Cd is the perpendicular bisector of both xy and st, and cy=20. find xy.

50 will mark show all use the linear combination method to solve the system of equations. explain each step of your solution. if steps are not explained, you will not receive credit for that step. 2x+9y= -26 -3x-7y=13

What are the solutions of the following system? y=-2x^2 y=x-2