The rate for internet access is 15 dollars per month plus 10 dollars per hour use. which function rule represents the monthly bill for x hours of use

Carli has 90 apps on her phone. braylen has half the amount of apps as theiss. if carli has three timesthe amount of apps as theiss,how many apps does braylen have? let b represent the number of braylen's apps and t represent the number of theiss's apps.