no 5 pakai cara .... .

L∆ = 1/2 . Alas . Tinggi
L∆ = 1/2 . 20 . 15
L∆ = 10 . 15
L∆ = 150 cm^2

L persegi panjang = l . P
L(Pp) = 20 . 10
L(Pp) = 200 cm^2

L seluruhnya = 350 cm^2