Yeah. I solved for the minimum value of D(x) (the function that gave the vertical height above sea level) and that ended up occurring at 1.5m. So I used his initial point (-10000 because it said D(x) was in metres) and 1.5 as the lower and upper bounds respectively and then differentiated D(x) to use in the arc length formula. I think you ended up getting a little over 10000 which I then divided by the speed (which I converted to m/s for consistency) to obtain time. I got around 15 minutes but I feel this is wrong because the answer otherwise seems very pointless. From the distance given (10km left) and the speed given (40km/h) even if you didn't apply this formula you would have got the same answer just by guessing. Anyhow, I'm super keen to see what the correct answer was because I'm sure there is more to it for the seven marks they were offering.