I have a textbox (txtInitialCost), textbox (txtCost), combo box (cmbNights), and a textbox (txtShared).

This is like someone staying at a hotel. There is an initial cost, the number of nights they stay, then number of nights shared. They only pay half price for each night shared (b/c the other person pays the other half).

I want txtCost to calculate a number for me from the values inside the other boxes. Let's say initial cost is $100, number of nights stayed is 2, and number of nights shared is 1.

It would calculate 100X2=200-(100/2) and would give me $150

This is initial value times number of nights = # - (initial cost divided by nights shared)

More help: Nights shared is Initial Cost/2 for each night shared. So if inital cost is 100 for 5 nights and 3 were shared. They pay half cost for 3 nights and full for 2. Which would equal $350 total cost.
100X2=200+(300/2) = $350

This is all screwed up in my head. But do you get what I am trying to do. If not I will try to right more clearly b/c these formulas aren't right.