Slope is

Then you use the equation

Where b is the y-intercept. To find it, plug in x and y from one of the points. Say, point 1 (1,10):

You know m (from above) and now you can solve for b.
Rearrange terms:

And that will be the answer.
Make sense?
Pretty sure when you multiply something by 0 it is 0 <span />
<span>length = 7x
</span><span>width = 2x
2(7x + 2x) = 72
7x + 2x = 72/2
9x = 36
x = 36/9
x = 4
</span>
width = 2x = 2 * 4 = 8 units<span>
</span>