Why must one side be zero when solving equations by factoring

Ana drinks chocolate milk out of glasses that each holdof a liter. she has of a liter of chocolate milk in her refrigerator. 10 how many glasses of chocolate milk can she pour?

The value of the expression 16-^3/4 8 1/8 -6 6 1/40 1/64

60 musicians applied for a job at a music school. 14 of the musicians play both guitar and drums. what is the probability that the applicant who gets the job plays drums or guitar?