0. 1x+0.5y+z=7

x+y+z= 15

Because X, Y, z y and Z are all integers and less than or equal to 10, x = 5；; y = 7； z=3

2. Set the distances of uphill, flat slope and downhill to x, y, z, y and z respectively.

x+y+z=3.3

x/3+y/4+z/5=5 1/60

x/5+y/4+z/3=53.4/60

x= 1.2

y= 1.6

z=0.5

3. Let the speed of car A and car B be x and y respectively.

15x+ 15y=600

60x-60y=600

x=25

y= 10

4. Suppose you buy X pieces from A and Y pieces from B. ..

2 10/x-700/y=3.5

25(x+y)-(2 10+700)=340

x= 10

y=40