F(1)=−6 f(2)=−4
f(n)=f(n−2)+f(n−1)


f(3)=f(3)=f, left parenthesis, 3, right parenthesis, equals

HURRY

F(3) = f(3-2) + f(3-1)
f(3) = f(1) + f(2)

then substitute using the values given so
f(3) = -6 + -4
so f(3) = -10

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