3. (20 points) Use implicit enumeration to find a feasible solution the following set covering problem instance (Do not complete the procedure, stop when you obtain a feasible solution). Provide the enumeration tree, and show all your work for each node of the enumeration tree. Branching rules: Start branching from the variable with the smallest index and go depth-first. When branching, set variable value to zero first. mins.t.x1+x2+x3+x4+x5x1+x21x1+x2+x51x1+x31x3+x4+x51x2+x3+x51x1,x2,x3,x4,x5{0,1} Show all your work