Answer: 14
Step-by-step explanation: The perimeter is all of the side added together. When finding the perimeter of a rectangle the opposing sides have the same value. So the equation would be 2(12) + 2(a) = 52. 12 x 2 is 24. 52- 24 is 28 and youre left with 28 = 2(a). You divide each side by 2 and get 14 = a