Lebar sungai (AB) adalah

Dikalikan silang
AB / 12 = 4/3
3AB = 12 × 4
AB = 12×4 ÷3
=16

BC/DE = AB/EC
12/4 = AB/3
4×AB = 12 ×3
4AB = 36
AB = 36/4
AB = 9
JADI, PANJANG AB = 9