14. Solve the following system of linear equation. x - 5y = 7 15y = 3x - 9

x - 5y  =  7                                                 -->      x -   5y  =  7  

15y = 3x - 9    (subtract 3x from both sides)  -->  -3x + 15y  =  -9

To cancel out the y-term, get both coefficients to by 15 by multiplying the top equation by 3:

                   x -    5y  = 7         (times 3)      -->    3x  -  15y  =  21

           (leave the second equation alone)      -->   -3x + 15y  = -9 

                   (add down the comumns)          -->     0x + 0y  =  12

This problem is impossible to solve because all the x's and y's disappear.

The first equation is:  3x - 15y  =  21; the second equation (after you multiply it by -1) is:  3x - 15y  =  9;

there is no way that 3x - 15y can be both 21 and 9; therefore, impossible.