no 17 18 pake cara ya

jumlah rusuk balok = 12
6,4 m =[(4 x p) + (4 x l) + (4 x t) ] x 5
640 cm = [(4x15) + (4x8) +(4xt)] x 5
640 = [60 + 40 + 4t] x 5
640 = [100 + 4t] x 5
640 = 500 + 20t
20 t = 640 - 500
20 t = 140
t = 140/20
t = 7 cm

mencari panjang kawat kerangka balok
= (4x11)+(4x8)+(4x5)
= 44+32+20
= 96

panjang rusuk kubus
= 96/12
= 8 cm