If the points (-1/2,0), (0,1/4), and (8,y) are collinear, then y= ? 
(The method is more important than the answer.)

simplistic way to look at it: as X increased by 1/2 between the first
two points, Y increased by 1/4, thus for each 1 unit increase in X, Y
increases by twice as much, or 1/2.

1/2 is called the "slope" of the line.

when X increases by 8 more units, Y will increase by 1/2 * 8 = 4, so
the y in the question will be 4 more than 1/4, or....

y = 4 1/4.  (4.25, if you like.)

there's a good discussion of lines & slopes in more depth at

http://mathforum.org/cgraph/cslope/

I found it by searching for "mx b", because the equation for a line is
often written as "y = mx + b", where m is the slope, 1/2 in this case,
and b is the "intercept", the value of y when x is zero, 1/4 in this
case.

I hope this is helpful to you.

--David

Thanks for the link.