Which of the following must be true?
a if |y| = 25 then y = 25 and y = -25
b if |t| = 40 then t = -40 only
c if |c| = 75 then c = 75 only
d if |u| = -40 then u = -40 and u = 40

The answer is C, when numbers or variables are between "|" (also called bars) it means to remove any negative symbols and think of it as a positive number. If the number is already positive you keep it a positive number.

Hello!
volume of sphere =4/3.pi.r^3