The formula for finding the perimeter of any rectangle is 2(width + length).
a) width= x ; length= x+7. Plug them into the formula 2( x+x+7). Combine like terms inside the parenthesis: 2(2x+7). Distributive property: 4x+14 is your answer.
b) Width=y ; length: 2y-1. Plug them into the formula: 2(y+2y-1). Combine like terms inside the parenthesis: 2(3y-1). Distributive property: 6y-2, is your answer.
I'm only doing the first two, the rest you should be able to do them.