While solving for unknowns from a set of equations, you have the chance to check your own work.
Following Jeff's example where he found x = 12 as the solution for the equation[ 9/4 * x - 2*x = 3], for checking we can replace 'x' by '12' in the left-hand-side of the equation and find out whether we get "3" as answer or not. If we do get the same answer then the solution is most probably correct.
9/4 * x - 2*x = 9/4 * 12 - 2*12 = 9*3 - 24 = 27 - 24 = 3
Thus if Jeff and I did not make "opposing" mistakes (which is impossible - we never make mistake) - then the answer is correct.
