Kim daivs has decided to buy cellular phone, but she is answer about which rate plan to choose. The " regular " plan charges fixed fee of 55% per month for 1000 minutes of airtime plus %0.33 per minute for any time over 1000 minutes. Executive plan charges the fixed fee of %100 per month 1200 minutes of airtime plus %25 per minute over 1200 minutes.
a. If kim excepts to use phone for 21 hours per month, which plan must she choose?
b. At what level of utilize would kim be indifferent between two palns?