Remark
You have to make up your own formula here. You also should estimate the answser. That's always good practice. It makes you think about Math.
Estimate
If you take 384,000 and estimate it to be 300000 and do the same with the diameter to make it 3000
300,000 / 3000 = 100 about. You should get an answer of 100
Formula
Distance to the moon (D)= number of moons (n) * diameter of 1 moon (di).
Givens
D = 384000
n = ??
di = 3476
Solution
384000 = n * 3476 Divide by 3476
384000 /3476 = n / 3476
n = 110.5 moons which I think you should like round to 110.
You could fit 110 moons in the given distance