Step 1: Calculate the total mass of the aircraft.
The question states that the aircraft has a 2 wheel nose gear and they
have given you the wheel load for a single wheel of 500kg they also say that
the single main wheel load is 6000kg's and you have 4 of those
2 x 500 =1000kg load on nose wheel
4 x 6000 = 24000kg load on the rear wheels
Total mass = 25 000kg
Step 2 Calculate the moment
1000 x 10 = 10 000 Moment of the nose wheel
Assume that the moment for the rear wheels have no moment i.e. factor of
0
Step 3 Calculate the arm = moment/mass
10 000/25 000 =0.4m or 40cm