15 points) Short answers. (a) When you solve an integer programming problem (suppose it is a maximization prob- lem), how do you obtain an upper bound on the optimal objective value? How do you obtain a lower bound? (b) Suppose you use a binary variable ya to represent whether or not event A will happen, and use a binary variable ys to represent whether or not event B will happen. How do you model the following logic constraint using an inequality? If A happens then B must happen (C) Suppose you use a binary variable yA to represent whether or not event A will happen, and use a binary variable ys to represent whether or not event B will happen. How do you model the following logic constraint using an inequality? Either A or B (or both) must happen