Plz help im going to fail if i don't get this

Show algebraically that f and g are inverse functions f(x)=x^2/-6; g(x)=square root of 2x+12

27 is what percent of 108? 27 is % of 108

The position of a moving particle is given by the position function: f(t)=-9t-t^2-0.2t^3+0.1t^4 0 a. at what time does the particle reverse direction? b. when is the displacement positive? (round one decimal place and answer in interval notation) c. when is the displacement negative? (round one decimal place and answer in interval notation) d. when is the particle’s acceleration positive? (round one decimal place and answer in interval notation) e. when is the particle’s acceleration negative? (round one decimal place and answer in interval notation)