[tex]\displaystyle
L_{_{D} }= 2 \times l_{_{D} } \\ \\
P_{_D} = 2L_{_{D} }+ 2 l_{_{D} }= 4l_{_{D} }+ 2 l_{_{D} }= 6l_{_{D} } \\ \\
l_{_{D} } = \frac{P_{_D}}{6} =\frac{60}{6} = \boxed{10 ~cm }\\ \\
L_{_P} = l_{_{D} } = \boxed{10 ~cm }\\ \\
P_{_P} = 4\times L_{_P} = 4\times 10 = \boxed{40 ~cm }
[/tex]
