solve by graphing

1.80+.2x=y
2.10+.15x=y

solve by graphing
20+20x=y
200-25x=y

Change to Slope intercept form: y=mx+b.

1.80 + .2x = y becomes:

y = .2x + 1.8 or y = 1/5x + 1.8

Slope: m = 1/5
the y-intercept is b.
In this case (0,1.8)

This means start at the point (0,1.8) and rise up 1 and run 5 to the right (5,2.8).
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Change to Slope intercept form: y=mx+b.
20 + 20x = y becomes:
y = 20x + 20

Slope: m = 20/1
the y-intercept is b. In this case (0,20)

This means start at the point (0,20) and rise up 20 and run 1 to the right (1,40).