Montgomery Reduction
Consult the transcript from the class, there is an example he works through which is very similar to this problem. Fundamentally you're trying to solve the problem c = (T + T(-N^-1) (mod R)N)/R (mod N). I suggest creating an equation in Excel (or other tool of your choice). Test your equation using the inputs from the example problem (EXAMPLE INPUTS: T=69, N=109, R=128, -N^-1 = 27). When you're confident your equation is working for that (EXAMPLE PROBLEM SOLUTION = 61), then plug in the values for this problem. Hint: T = 25 for this problem.