Answer:
The length of the rectangle is 15 cm.
Step-by-step explanation:
breadth(b)=?
length(l)= 3+2b
perimeter(P)= 42 cm
Now,
P = 2 ( l+b )
or, 42= 2 ( 3+2b+b)
or, 42 = 2 ( 3+3b)
or, = 3+3b
or, 21 = 3+3b
or, 21-3 =3b
or, 18 = 3b
or, = b
or, 6 = b
Here, Breadth(b)= 6 cm
Length (l) = 3 + 2*6
= 3 + 12
=15 cm