Question 452224
3x+9y=21
-8x+y=19
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You assume the x's mean the same in both
equations and the y's mean the same in
both equations.
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So you solve one of the equations for one of 
the variables:
For example: y = 8x+19
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You substitute that expression into the other
equation in place of "y" to get an equation
with only the variable "x".
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3x + 9*(8x+19) = 21
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Divide thru by 3 to get:
x + 3(8x+19) = 7
x + 24x + 57 = 7
25x = -50
x = -2
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Now you can solve for "y":
y = 8x+19
y = 8*(-2)+19
y = -16+19
y = 3
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Solution for the system of two equations: (-2,3)
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Cheers,
Stan H.
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