Answer:
(x, y) = (5, -1)
Explanation:
First of all, look at the equations. The first would be in standard form if it were divided by 10. (Here, we're calling this process "normalization," for lack of a better term) Doing that gives coefficients of 3, 5, 10. The second would be in standard form if divided by 3. Doing that gives coefficients 1, -5, 10.
At this point, you observe a couple of opportunities to use elimination to solve these equations. Since the x-coefficients match after the first normalization, we can subtract one equation from the other at that point. (That is what we did below.)
Since the y-coefficients are opposites after the second normalization, we could simply add the two equations to eliminate y. Either way rapidly gets you to an answer.
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Choose an approach and work the problem
Divide the first equation by 10 and subtract the second equation.
... (3x +5y) -(3x -15y) = (10) -(30)
... 20y = -20
... y = -1
From either equation we can find x. Using the second one ...
... 3x -15(-1) = 30
... 3x = 15 . . . . . . subtract 15
... x = 5 . . . . . . . . divide by 3