An even number minus an even number

The fence around a quadrilateral-shaped pasture is 3a^2+15a+9 long. three sides of the fence have the following lengths: 5a, 10a-2, a^2-7. what is the length of the fourth side of the fence?

Sam is picking fruit from a basket that contains many different kinds of fruit. which set of events is independent?

Which best describes a central bank's primary goals? limiting inflation and reducing unemployment reducing unemployment and maintaining cash flow controlling stagflation and reducing unemployment managing credit and ensuring the money supply's liquidity