解：86×18+21ⅹ12=43×2×3×6+21×12=（43×3）×（2×6）+21×12=129×12+21×12=（129+21）×12=150×12=50×36=1800
86x18+21x12=43x2x2x9+3x7x3x4=（43+7）x36=180
