Consider the following branch and bound tree $($minimization problem of MILP$),$

i$-$ What is the tightest lower and upper bound found so far?

ii$-,$ Which nodes can be pruned and which must be explored further?

Note: Next to each node, the upper value represents the value of the objective function if the solution

of the relaxation is feasible in the original problem. Also, the lower value represents the value of the

objective function when solving the relaxation associated to the node.