应该是400过程 简便计算3.6×31又2/5+43.9×6又2/5+6=3.6×31+3.6×2/5+43.9×6+43.9×2/5+6=（3.6×31+43.9×6）+（3.6×2/5+43.9×2/5）+6=（111.6+263.4）+【2/5×（3.6+43.9）】+6=375+2/5×47.5+6=375+19+6=400