Using the linear combination method, what is the solution to the system of linear equations 5x+3y=-10 and -20x-7y=15

The x-coefficients have a nice ratio, and one of them is negative. That makes it easy to eliminate x by multiplying the first equation by 4 and adding the second equation:

4(5x+3y) +(-20x-7y) = 4(-10) +(15)

5y = -25 . . . . . simplify

y = -5 . . . . . . . divide by 5

Substitute this result into either equation to find x. I choose to use the first equation.

5x +3(-5) = -10

5x = 5 . . . . . . add 15

x = 1 . . . . . . . divide by 5

The solution is (x, y) = (1, -5).

the answer is b.)

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