4X7/2+4X9/2+7/5X4 =4X(7/2+9/2)+7/5X4=4X8+1.4X4=32+5.6=37.6
第二道题目我想你写错了.
(1/3-1/5)X45=1/3X45-1/5X45=15-9=6.