Question

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Answer 1

Multiply each equation by something to get one variable the same.
(3x+4y=1)(3)=9x+12y=3
(5x-3y=-21)(4)=20x-12y=84
Add the equations.
29x=87
Divide by 29.
x=3
Plug x into one of the equations and solve for y.
9+4y=1
Subtract 9 on both sides.
4y=-8
Divide by 4 on both sides.
y=-2
Solutions:
x=3
y=-2

Answer 2

That is explained.

Answer 3

Not really.