no 6 ,tlng buat bsk,please

P= 2L -3
Kll = 2(P+L)
18= 2(2L-3 + L)
18= 2(3L-3)
9= 3L-3
12=3L
L= 4
P=2L-3
P= (2 x 4) - 3
P= 5
Luas = P x L
= 5 x4 = 20 cm