Question

To eliminate the y-terms and solve for x in the fewest steps, by which constants should the equations be multiplied by before adding the equations together?

First Equation: 5x − 4y = 28

Second equation: 3x - 9y = 30

The first equation should be multiplied by 3 and the second equation by 5.
The first equation should be multiplied by 3 and the second equation by −5.
The first equation should be multiplied by 9 and the second equation by 4.
The first equation should be multiplied by 9 and the second equation by −4.

Answer 1

Multiply the first equation by 9 and the second by −4.

9(5x − 4y) = 9(28) → 45x − 36y = 252
−4(3x − 9y) = −4(30) → −12x + 36y = −120

Add: 33x = 132 → x = 4.