Question

Find the perimeter of ABC.

Answer 1

You times 12ft by 3 because to get to 5ft to 15ft you multiply 5 by 3

Answer 2

If two shapes are similar, they are scaled by some factor. In other words, you have

$AB = k\cdot ED,\quad AC = k\cdot DF,\quad BC = k\cdot EF$

In particular, we know that

$BC = 15 = k\cdot 5 = EF$

And we deduce $k=3$

So, the perimeter of ABC is

$AB+BC+AC = 3ED+3EF+3DF = 3(ED+EF+DF)$

So, the perimeter of ABC is three times the perimeter of DEF, and thus it's

$12\cdot 3 = 36$ feets