Answer:
138 is the answer
Explanation:
In order to find the perimeter, we use this formula
P=2(l+w)
And to find the width, we use this formula
w = P/2 - L = 18/2 - 3 = 6
So the width is 6
3 × 6 = 18
So thats why the perimeter of the top triangle is 18
We do 21 ÷ 3 = 7, 7 = scale factor
To find the perimeter of the bottom triangle, we do
the width of the top rectangle times 7
so 6 × 7 = 48
So the perimeter for the bottom triangle is
P=2(l+w)=2·(48+21)=138