Hey there!
To start, substitution is isolating one variable in one equation in a system and plugging it into the second equation for the variable isolated.
In this case, because y in the first equation has a coefficient of 1, it is easiest to use. So now, isolate y:
-8x + y = -6
y = 8x - 6
Now that you have solved for y, plug 8x - 6 into the y value of the second equation and solve for x:
16x + 2(8x-6) = 3
16x + 16x - 12 = 3
32x - 12 = 3
32x = 15
x = 15/32
Now that you have your x value, plug it into your first equation for x and solve for y:
-8(15/32) + y = -6
-15/4 + y = -6
y= -6 + 15/4
y= -9/4
Therefore, your final answer would be x = 15/32 and y = -9/2 or the point pair (15/32, -9/2).
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