You are not the only person asking for hints on that particular problem set. There are two other people as well, but your solutions look quite different. Without seeing the exact question/setup, it is impossible to tell what is going on. My hunch is that the confusion/problem comes from what is actually predetermined in the model. Clearly, capital is predetermined, but so is usually the aggregate money stock. At the same time, its unclear to me whether the division of the aggregate money stock into cash and deposits is predetermined as well or can be decided within the period. Put differently, what is the relation between M_t,m_{c,t},m_{d,t}?
Is it
M_t=m_{c,t}+m_{d,t}
or
M_{t-1}=m_{c,t}+m_{d,t}
Relatedly, see Timing of capital in two sector model