Zoot Chimney Sweeps has determine their monthly revenue is governed by the equation R(x)=150x-(x^2/30), where X is number of chimneys cleaned, and R(x) is monthly revenue in dollars. Differentiate R(x) with respect to T, and determine the rate of change of revenue if x=45 and (dx/dt)=3 chimneys per month. Explain your results.