Remember
a HSI gives a horizontal illustration of where the displaced line is in
relation to the aeroplane, and you can turn it round unlike a
OBI which is displaced from the top of the instrument
So the aircraft is heading 160. The aircraft is on a 240 radial from a VOR.
Draw it out. The aircraft is in effect heading away from the radial toward the
bottom right of a page assuming the top is North. If
the aeroplane had 240 selected on the HSI it would cut straight through the
aeroplane and show no deviation. BUT the question states the selected course is
250, which is a radial further north and further 'behind' the aeroplane in
relation to its heading.