First, needs a diagram.
1) Blue line at bottom representing
1023hPa pressure level.
2) Hill on top the dotted line, a
little mark on top of hill representing airfield.
3) Red line part way up the hill
representing 1013hPa pressure level.
4) Red Line somewhere well above the
hill representing 7500 feet.
Ok, now for the calculations -
distance between bottom of hill (1023 level) and top is 1500ft (draw an arrow
representing this).
Distance (height) between 1013
pressure level and FL75 is 7500ft.
Height difference between 1023 and
1013 pressure levels is 300feet.
Therefore, you can infer that top of
hill is 1200ft above 1013 level.
Final step - height of FL75 above top
of hill should be fairly clear from the diagram - 6300feet.
As temperatures are ISA no correction
is needed, so that should be the answer.