In order to find the deposit Leory needs to make, let's use the following formula for compound interest:

Where C is the final value, A is the initial value, i is the interest rate, t is the time and n is a constant related to the period of interest.
For this case, we have C = 1000, i = 10% = 0.1, n = 12 (the interest is compounded monthly), and t = 3, so we have that:

So the initial deposit is $741.74.