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<p>Wrong, solving a system would be very helpful. This is what many people fail to see. There is a constraint on every variable… they must be an integer element of the interval [0,9] which means putting the equations in terms of one variable was very helpful.</p>
<p>As I pointed out before, it allows you to determine the value of y as 4 and then you can do the rest through the original equations.
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<p>I hope I didn’t come off as too brusque. If I did, sorry. :D</p>