7/9-7/9×3/5+2/蔽搏5=7/9×（1-3/5）+2/段档5=7/9×2/5+2/5=（1+7/9）×2/5=16/握并乱9×2/5=32/45
7/好模9-7/9x3/5+2/5＝7/9x（饥芦1-3/5）+2/5＝7/9x2/5+2/5＝2/5x（7/9+1）＝2/友肢缓5x16/9＝32/45
