x- 18=(x-6)5/8

x- 18=5/8x- 15/4

3/8x= 14 and 1/4.

x=57/4×8/3

x=38

There are 38 bags of flour and 38 bags of rice in the canteen.

2、 18÷( 1-5/7)

= 18×7/2

=63

63÷ 18=3.5 liters

The volume of each tank of water is 3.5 liters.

3, 60+60×25%=75 yuan

60-60×25%=45 yuan

60×2-(75+45)=0

These two clothes didn't make a profit or lose money.

4、=2009×(2000+ 10)/20 10×(3000- 1)+2009

=40 18000+20090/6030000-20 10+2009

=4038090/6029998

=20 19045/30 14999

≈0.67

5、=6/ 12+2/ 12+ 1/ 12+ 1/20+ 1/30+ 1/42

=9/ 12+ 1/20+ 1/30+ 1/42

=45/60+3/60+2/60+ 1/42

=5/6+ 1/42

=35/42+ 1/42

=36/42

=6/7