Because of relative high interest rates, most consumers attempt to pay off their credit card bills promptly. However, this is not always possible. An analysis of the amount of interest paid monthly by a bank's Visa cardholders reveals that the amount is normally distributed with a mean of $27 and a standard deviation of $7.

a) What proportion of the bank's Visa cardholders pay more than $30 in interest? (Carry answer to the nearest ten-thousandths)

b) What proportion of the bank's Visa cardholders pay more than $40 in interest? (Carry answer to the nearest ten-thousandths)

c) What proportion of the bank's Visa cardholders pay less than $15 in interest? (Carry answer to the nearest ten-thousandths)

d) What interest payment is exceeded by only 20% of the bank's Visa cardholders? (Carry answer to the nearest hundredths)