It takes Alisa ten minutes to fill a dozen water balloons. She wants to calculate how long it will take her to fill all the water balloons if each friend at her party gets a dozen balloons. What variable is needed to calculate the time it will take to fill all the balloons?
A. s, the number of students in Alisa's math class
B. d, the amount of time it takes Alisa to fill a dozen balloons
C. f, the number of friends attending Alisa's party
D. b, the number of bags of water balloons Alisa bought