To find this cache you will need to have visited the Exeter Arts Trail 1 Adventure Labs.
I advise doing the stage of the Adventure Lab that is furthest away from the other 4 last as the bonus is nearest to that one.
Along with the answer to each question you will have found the values for letters A, B, C, D, E, F, G, H, J and K.
Using these values in the following formula you will get the coordinates for the Bonus cache hide itself.
N50 AB.CDE W003 FG.HJK