Assignment problem and branch and bound

A factory produces a certain type of car parts. There are four alternative machines that can be used for the production of the car parts from start to finish. Each of the machines needs to be controlled by an individual operator. The operators have different efficiencies on different machines. The table below shows how many car parts the individual operators produce in average per day. Furthermore, this table shows how many erroneous parts the individual operators produce in average. Your task is to find out where the operators should be placed such that they produce as many as possible car parts. At the same time, the number of erroneous parts should not exceed 4 % of the total production.

Production per day:

	Machine A	Machine B	Machine C	Machine D
Operator 1	18	20	21	17
Operator 2	19	15	22	18
Operator 3	20	20	17	19
Operator 4	24	21	16	23
Operator 5	22	19	21	21

Number of erroneous parts per day:

	Machine A	Machine B	Machine C	Machine D
Operator 1	0,3	0,9	0,6	0,4
Operator 2	0,8	0,5	1,1	0,7
Operator 3	1,1	1,3	0,6	0,8
Operator 4	1,2	0,8	0,6	0,9
Operator 5	1,0	0,9	1,0	1,0

For health reasons, operator 1 needs to be placed on machine 1. Draw a sketch that can used as a departing point for a branch-and-bound approach that solves this problem more efficiently than brute force (brute force means that we evaluate all possible solutions).