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HELP PLEASE!!!! SHOW WORK!!!
7) Kristof wants to build a new rectangular pen for Sven to live in. Kristof measures and finds that the width of the fence is 3x + 4. He also knows that he wants the length of the fence to be 4 times the width.

a) Create an expression that could be used to find the perimeter of the fence.
b) If Kristof knows that the perimeter of the fence is 280 feet, what is the length and width of the fence?