Question 488139
I don't think the question came out as you intended, The way you have put this you need a constant that relates the two congruent sides to the third side.
if you let y = the congruent sides,
C = the constant
x = the non-congruent side,
P = perimeter.
You can set up an equation y = Cx; C will be different in each each example.
so our equation is perimeter (p)

f(x) = 2y  + x.
So, for your example, C=5.
2(5x) + x = 11x, your perimeter.
Cleomenius.