I believe the answer is $33.60?
By the chain rule,

It looks like we're given

where <em>a</em> and <em>b</em> are presumably constant.
Recall that


so that

Then we have




where the last reduction follows from dividing through everything by
and simplifying.
I'm not sure at which point you're supposed to evaluate the derivative (22/7*4, as in 88/7? or something else?), so I'll leave that to you.
<span>The distance from the vertex to the centroid is twice the distance from the centroid to the side.
This means that 3x + 5 = 2 * (2x)
</span><span>3x + 5 = 4x
x = 5
Source:
http://www.1728.org/trictr.htm
</span>
Hey number 8. Be super careful, less than always look at that it should be 5n-3