Question

solve by addition
5x+3y=-1
x+y=1

Answer 1

y = 3, x = -2

Answer 2

If you want more than a mere answer without any explanation, here goes

We have to eliminate a variable. To do so we need to multiply a constant

Let's eliminate y

Multiply second equation by -3, we get
-3x-3y=-3
add that to first equation
5x+3y=-1
-3x-3y=-3
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2x=-4
x=-2

Find y by plugging in value of x