supyan
No a) L= p x l........600cm^2= 20cm × (x+12)cm......(x+12)cm=600cm^2/20cm=30cm.........(x+12)cm=30cm...........x=30cm-12cm..........x=18cm.......... no b)panjang=20cm.........lebar=(x+12)=(18+12)=30cm.........Keliling=2(p+l)=2(20cm+30cm)=2(50cm)=100cm