That tutor did it an easier way. He was able to because the numbers
were easy.  But if they hadn't been, this is how you would do it:


Let x = the number of minutes
Let y = the number of words typed.

Then,
when x = 3, y = 174, and
when x = 6, y = 348

So we find the equation of the line through the two points
(3,174) and (6,348)

First we use the slope formula:

Slope formula:
m = 
where (x1,y1) = (3,174)
and where (x2,y2) = (6,348)

Then the point-slope formula:

Point-slope formula:
y - y1 = m(x - x1)
where (x1,y1) = (3,174)
and where the slope m is the value you got from 
the slope formula

Then when you get the equation, solve for y,

Finally, substitute 8 minutes for x, and simplify and that
will be the answer.

Edwin