The average commission c (in dollars) per trade by an investment corporation decreased as more of its customers traded online, according to the formula

\(\displaystyle c(u) = 100u^2 - 160u + 110\) [units are dollars per trade] [u = fraction of trades done online]

During that time, the fraction of online trades increased according to

\(\displaystyle u(t) = 0.42 + 0.02t\) [t = months since January 1, 1998]

Use direct substitution to express the average commission per trade c as a function of time t (do not just simplify the expression) and then use the chain rule to derive the formula for estimate the rate of change of average commission per trade. Use this formula to estimate the rate of change of average commission per trade at the beginning of October, 1998.