4x-6y-z=-15,3x+y-z=-1,5x-y-z=-11
Use elimination, the y's are perfectly set up for it
1st - 2nd ----> x - 7y = -14
3rd - 1st ----> x + 5y = 4
now subtract those two to find y, then sub back into x+5y = 4
and finally into one of the originals.
hint: z will be an integer, the other two are simple fractions.