Math
posted by Jennifer .
The maximum weight M that can be supported by a beam is jointly proportional to its width w and the square of its height h, and inversely proportional to its length L.
a. Write an equation that expresses this prportionality
b. Determine the constant of proportionality if a beam 4 in. wide, 6 in. high, and 12 ft long can support a weight of 4800 lb.
c. If a 10ft beam made of the same material is 3 in. wide and 10 in. high, what is the maximum weight it can support?
So far, I've got the equation. It's M=k^2wh^2/L. I need help working out the problem.

M=k*wh^2/L
I don't know why you squared k, the constant.
4800=K*4*36*12 note units in*in^2*ft
k=100/36
M=100/36*3*100*10=100,000/36=? 
the weight that a beam can support varies inversly as the length,suppose a 12 foot beam can support 12000 pounds how many pounds can a 15 foot beam support