Find dy du and dy du dx dx (a) y = u' and u = x2 + 2 dy du du dx = dx (b) y = u and u = 7x2 - x+ 4 dy = du du E dx dx\fIf an IRA is a variable-rate investment for 15 years at rate r percent per year, compounded monthly, then the future value 5 that accumulates from an initial investment of $1000 is 180 s = 1000[1 + 0'0\"] . 12 What is the rate of change of S with respect to r and what does it tell us if the interest rate is as follows? (Round your answers to two decimal places.) (a) 6% If we were to increase the rate by 1%, the future value of the investment would increase by about $ . (b) 12% If we were to increase the rate by 1%, the future value of the investment would increase by about $ :]