22 The loudness, L, of a sound in decibels (dB) can be calculated using the formula _ = 10 log - , where / is the intensity of the sound in watts per square metre W ) and 1 = 10-12 W . A singer is performing to a crowd. Determine the intensity of the singers voice if the sound level is 90 dB. 23 How many years will it take for a $400 investment to grow to $1000 with a interest rate of 12%/a compounded monthly? 24 . Discuss why exponential equations of the form f(x) = ab" always have positive instantaneous rates of change when a is positive and b is greater than one, and why they always have negative instantaneous rates of change when a is positive and b is between 0 and 1