X=29 and y=10
You would isolate one of the variables and then plug the expression into the other equation to find the value of one variable. Then you would plug this value into the other equation to determine the value of the remaining variable.
So our original equations would be..


(a) perimeter in terms of y

(b) area in terms of y
*I'm actually not sure about b.. sorry*
(c) if perimeter = 28, find length


C is the correct answer
C is the only option in which the original shaped can be multiplied and get another one.
explanation:
look at the dimensions of the original shape, 1x5x3
look at the dimensions of C,
2x10x6
multiply the original by 2 and the answer is C it is the only one that is consistant
With two equal sides it’s called isosceles triangle