Step-by-step explanation:
the scaling ratio is 12/20 = 3/5.
this always applies only to one-dimensional distances, lengths.
the perimeter is calculated as the sum of individual lengths. so while each length is scaled by the same ratio, also the sum is then scaled by that ratio.
p_old = a + b + c
p_new = ra + rb + rc = r(a + b + c) = r×p_old
so, the ratio for the perimeter is also 3/5.
for the area this is a bit different, as an area is always calculated by multiplying 2 lengths (other unscaled factors can be ignored for that consideration of relative change), and that means the scaling ratio has to be multiplied in twice.
a_old = a × b
a_new = ra × rb = r² × a×b = r² × a_old
so, the ratio for the area is
(3/5)² = 9/25
