B. parallelogram is the answer
A scalene triangle is one whose sides are all a different length. So there is no way you can find the length of b when you are only given the length of a and the perimeter.
x + 13 = 7x+1
Subtract x from both sides:
13 = 6x +1
Subtract 1 from both sides:
12 = 6x
Divide both sides by 6:
x = 2