The only error you made is on problem 3. Everything else is correct. Nice work.
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Here is how to solve problem 3
Plug x = 1 into the equation and solve for y
-3x + y = 1
-3*1 + y = 1 ... replace x with 1
-3 + y = 1
y - 3 = 1
y - 3 + 3 = 1 + 3 .... add 3 to both sides
y = 4
The answer is 4
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Verifying the answer:
Plug (x,y) = (1,4) into the equation. Both sides should be the same number after simplifying both sides.
-3x + y = 1
-3*1 + 4 = 1 ..... replace x with 1; replace y with 4
-3 + 4 = 1
1 = 1
The answer is confirmed.
If you were to graph -3x + y = 1, which is equivalent to y = 3x+1, you'll find that the point (1,4) is on this line.
