please help me with the last two questions

Which of the following is not an assumption underlying cost-volume-profit analysis? a. The sales mix is constant b. The break-even point will be passed during the period. Cc Corts can be accurately divided into fixed and variable components d. Total sales and total costs can be represented by straight lines, Xander Studios holds a sculpting class for which it charges students $250. The costs consist of the following: Variable costs per student: Sculpting supplies $100 Enrollment costs SO Fixed costs for the course Instructor's salary $1,000 Rental cost of the classroom 500 The break-even number of students is a. 11 Cb2 c. 12 d. 20