Divide the two known corresponding sides: JK/AB = 18/12 = 3/2 = 1.5
So the sides of triangle JKL are 1.5 (one and a half) times bigger than the corresponding sides for triangle ABC
1.5 is the linear scale factor
This extends to the perimeter as well:
perimeter of JKL = 1.5*(perimeter of ABC)
perimeter of JKL = 1.5*28
perimeter of JKL = 42 feet
It turns out that since the linear scale factor is 1.5, this means the area scale factor is (1.5)^2 = 2.25
The new area is found by multiplying the old area by 2.25
area of JKL = 2.25*(area of ABC)
area of JKL = 2.25*18
area of JKL = 40.5
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In summary:
Perimeter of JKL = 42 feet
Area of JKL = 40.5 square feet