Please show the handwritten process for this ILP model

Problem 1: A large drug company must determine how many sales representatives to assign to each of four sales districts. The cost of having n > 1 representatives in a district is ($88,000+$80,000n) per year. (The cost of having 0 representatives in a district is $0 per year.) If a rep is based in a given district, the time it takes to complete a call in another district is given in the following table, where times are in hours: 4 7 4 Rep's Base District 1 2 3 4 Call District 1 2 3 1 4 5 4 1 3 5 3 1 7. 5 2 5 1 2 Each sales rep can work up to 160 hours per month. Each month the following number of calls must be made in each district: District 150; District 280; District 3100; District 460. A fractional number of representatives in a district is not permissible. Formulate an integer-linear program to determine how many representatives should be assigned to each district