Find the y intercept of the lines.

-10x + 5y = 40

5x + 4y = 80

-10x + 5y = 40
+10x +10x
5y = 40 + 10x
÷5 ÷5
y = 8 + 10/5x simplify (10 ÷ 5, 5÷5)

y = 2x + 8


5x + 4y = 80
-5x -5x
4y = 80 - 5x
÷4 ÷4
y = 20 - 5/4x

y = 5/4x + 20


*Note* Whatever sign is in front of the number (positive/negative) is what you use (adding/subtracting)

The answer to your question is -10x + 5y = 40  is  y = 2x + 8
                                                     5x + 4y = 80  is  y = 5/4x + 20

Hope this helps.

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