Which of the following is rational number square root of 15 square root 16 square root 21 square root 22

By definition, a rational number can be expressed as a fraction that either ends or repeats.  A rational number could also be in the form of any number over 1, cuz it divides out to give the number back.  The only one above that is rational is sqrt 16, because it simplifies to 4, which as a rational number, could be expressed as a fraction:  4/1

If you need an equation, it would be y=2x+8, y would be how long it grew, x being weeks.if you need how long he was asleep, it would be 4 weeks if he started with no beard, the equation would be x=8÷2if he did have a beard before hand, the equation would be 2w+x=8