X-3y=0 can be obtained from two formulas: x=-3 and y=- 1.

2、3x+4y=-6

The original formula = 6x+8y+15 =-12+15 = 3.

3、2(x+y)= 1

6(x-y)= 1

x = 1/3； y = 1/6； Party A and Party B run each minute1/3; 1/6 laps

4 、( k-3)x & gt； -7

Obviously, when k=3, there is always 0 >; seven

5.M