Someone help me out I thought I knew how to do this

Solve 3x-18=2y and 5x-6y=6 by elimination show work

Which of the following statements would be sufficient to prove that parallelograms pqrs is a rectangle ?

The motion of a weight that hangs from a spring is represented by the equation h=8sin(2pi/3t). it models the weight’s height above or below the rest position as a function of time. approximately when will the object be 3 inches above the rest position?