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.