2, 6-1= 55+4+3+2+1=15 times.

3,5+4+3+2+1=1515× 2 = 30 sheets.

4.20×2÷(85-75)=4 hours (85+75)×4=640 kilometers.

5,4/5: 3/8 = 32:15 is 32/ 15 of B.

6. 1/8×7 = 7/8 2×7 = 14kg 14÷( 1- 1/8)= 1 12kg。