Atable of values of a linear function is shown below. find the output when the input is n.

input 1 2 3 4 n
output -4 0 4 8 ?

As the input (x) increases by 1, the output (y) increases by 4.  When x is 0, y would be -8.  The equation for this table of values would be y = 4x - 8.
If n was 5, we would multiply it by 4 to get us 20.  20 subtracted by 8 is 12.  The answer would be (5, 12).  This is correct because the output increases by 4 again, making it a linear function.

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