Răspuns :
P=3dm
P=30cm
P=2l+2L
2l+2L=30cm
l+L=30cm:2
l+L=15cm
L=6cm
l+6cm=15cm
l=15cm-6cm
l=9cm
P=30cm
P=2l+2L
2l+2L=30cm
l+L=30cm:2
l+L=15cm
L=6cm
l+6cm=15cm
l=15cm-6cm
l=9cm