Respuesta :
Answer:
The answer is 3cm
Please give branliest!
Step-by-step explanation:
(S1×2)+(S2×2)=21cm
(S1+S2)×2=21cm
S1+S2=21÷2
7.5+S2=10.5
S2=10.5-7.5
S2=3
Breadth=3cm
Step-by-step explanation:
p=2(l+b)
21=2(7.5+b)
21=15+2b
21-15=2b
6=2b
6/2=b
b=3