Given the function defined, find the average rate of change

On a trip, you had to change your money from dollars to british pounds.  you got  560  pounds for  800  dollars.  which is a unit rate that describes the exchange

Anyone know? will mark brainliest if you're correct!

The position of a moving particle is given by the position function: f(t)=-9t-t^2-0.2t^3+0.1t^4 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)