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Work Shown:
x = number of hours spent running
8x = distance he runs (since he runs at 8 mph)
y = number of hours spent walking
3y = distance he walks (he walks at a speed of 3 mph)
8x+3y = total distance = 16 miles
8x+3y = 16
This equation is in standard form Ax+By = C
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Extra Info
Solving for y will get
8x+3y = 16
3y = -8x+16
y = (-8x+16)/3
y = (-8x)/3+16/3
y = (-8/3)x+16/3
This is in slope intercept form y = mx+b
m = -8/3 is the slope
b = 16/3 is the y intercept