Question

A box with a volume of 40 cubic inches holds 10 balls. A box with a volume of 60 cubic inches holds 15 of the same kinds of balls. Assume the relationship is linear. Which equation models the relationship between the volume, x, and the number of balls y ?
A).y=0.25x+10
B).0.25x
C).y=4x
D).y=4x+60

Answer 1

Pretend these are coordinates that you can use to find the slope of the line.
(10, 40) and (15, 60). Fit these into the slope formula to find the slope of the line you are looking for:
$m= \frac{60-40}{15-10}$ and the slope is 4. Now use one of the points and the slope of 4 to solve for b, the y-intercept:
40 = 4(10) + b so b = 0.  The equation of the line then is y = 4x + 0 or just
y = 4x