Respuesta :

sledgehammer08

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

gracie9779

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