Judging from the meaning of the question,

By matching the coefficients a and b with two equations, the following equation can be obtained.

a(7x+3y)=5a.....①

b(3x-y)=b........②

1+2,

x(7a+3b)+y(3a-b)=5a+b

And want to 5x-y, can be obtained by observation.

7a+3b=5，3a-b=- 1

Get a solution,

a= 1/8，b= 1 1/8。

So substitute 5a+b=2.

Answer over

Passerby products, if satisfied, please use the speed of light, dear.