In the Bank Location problem, four of the twenty counties were on adjacent to Pennsylvania. (Counties 1, 14, 15, 16.) If the bank president wanted to be sure that at least one bank was located in one of these counties, what constraint would need to be added to the model?
a. x1 + x14 + x15 + x16 > 1
b. x1 + x14 + x15 + x16 >= 1
c. x1 + x14 + x15 + x16 = 1
d. x1 + x14 + x15 + x16 <= 1