What is the optimization model of this problem :

 

The company providing HW and SW for its clients, received an offer for 3 new projects A, B, and C. It is the development and implementation of SW and subsequent SW maintenance for the same period as the length of the project. For how many months should the company conclude the first contracts for these projects with regard to their revenues with constraints by their complexity and job opportunities? In total, the company has at most 109 MD (mandays) available for these projects. Project A requires 12 MD, project B 12 MD and project C 10 MD per month. In the future, a monthly SW maintenance yield is supposed for project A of 9 thous. CZK, for project B 8 thous. CZK, for project C 10 thous. CZK. For projects together, the planned revenues for SW maintenance are at least 174 thous. CZK. The total cost of projects can be at most 200 thous. CZK. Monthly costs for individual projects are in a row 12 thous. CZK, 12 thous. CZK and 10 thous. CZK. Total revenues for accepted projects should be maximal. Monthly revenues for individual projects are in a row 15 thous. CZK, 12 thous. CZK and 22 thous. CZK