Raymond B. answered 21d
Math, microeconomics or criminal justice
do row operations until you get 1's in the diagonal and 0's everywhere else. in the first 6 columns. then the solution will be in the last, 7th column
but that's impossible as it's not a square matrix
so, you get an infinite number of solutions
a -4b +4y = 2
c -5y = -2
x + 2y = 0
z = 3
6 variables, only 4 equations, no unique solution except for z=3