Need some quick code for calculating output hours

Hello Guys,

If someone could help me get started on a small piece of code that I am writing, that would be great.
Here is the problem.

I have months ( 1 to 12 ). Every month, a set of tasks need to be executed which takes "x" number of hours.
So if I have 1 machine working 3 hour in the month 1, the total time spent is 3 hours. Fairly simple right !

But here is where it starts to get a little tricky.
Say on month 2, a set of tasks take 4 hours. total time that my first machine takes is 4 hours. But i want to introduce 3 new machines
in this month, which will execute the first month's tasks. So total time spent here is ( 3*3 + 4*1) = 13

On month 3, task time is 6 hours. And I am introducing 2 new machines.
So total time is 2*3 ( time taken for 2 new machines to perform first month's tasks ) + 3 * 4 ( 3 new machines introduced last month will now execute second months task) + 6 * 1 ( time the first machine will spend on month 3 s tasks ) = 24

I need a VBA macro which can help me get started on this.
Any help will be appreciated !
I have attached a spreadsheet which forumla's in the section "output hours" but that column will need to replaced with the actual outputs from the VBA code.