Can't be solved. 3 variables (x, y, z) needs 3 equations most of the time. This problem only has 2 equations.
Note: It could be solved with just 2 equations if any of the ratios for any of the variables were the same. 5/3 for x, -12/-7 for y, and 7/4 for z (140/84, 144/84, 147/84 if you want matching denominators) are all different, so that doesn't work in this problem.
Need 3 equations.