7/13+16/9+6/13-8/9
=(7/13+6/13)+(16/9-8/9)
=1+8/9
=17/9;
（3/4-3/4*2/5）/1/5*5
=(3/4)×(1-2/5)×25
=(3/4)×(3/5)×25
=45/4;
4/5*（X-2/5）=8
x-2/5=10;
x=10+2/5;
x=10.4;
如果本题有什么不明白可以追问,