balok dengan luas alas 112cm2, panjang 14cm, tinggi 5cm, jadi luas permukaannya adalah

La = p x l
112 = 14 l
l = 112/14
l = 8 cm

Lp = 2 x (pl + pt + lt)
Lp = 2 x (La + pt + lt)
Lp = 2 x (112 + 14x5 + 8x5)
Lp = 2 x (112 + 70 + 40)
Lp = 2 x 222
Lp = 444cm²

penyelesaian:
La = p x l
112 = 14 x l
l = 112 : 14
l = 8 cm

Maka;
Lp = ( 2 x p x l ) + ( 2 x p x t ) + ( 2 x l x t )
Lp = ( 2 x 14 x 8 ) + ( 2 x 14 x 5 ) + ( 2 x 8 x 5 )
Lp = 224 + 140 + 80
Lp = 444 cm²