2.- 1+a

3.20

4.2 1.6

5. 10x+(40-x)*8=370

6. 18

Application:

1. Set X and Y ... equations:

y=2(x-3)，2400x+3300y= 1 15200

X= 15 y=24。

2.( 1-3/30)*20 = 18 hours

3. This problem can be divided into the sum of the time before and after the U-turn of 1.

The time before U-turn is 10/45= 13.33 minutes.

Travel time in the opposite direction [10-(10/45 * 35)]/(35+45) =1.67 minutes.

The total time is13.33+1.67 =15 minutes.