Bill likes both Red Bull (x₁) and Monster (x₂) energy drinks.Both help him stay awake to finish his microeconomics homework, so they're perfect substitutes. His preferences over the drinks can be represented by utility function U(x₁, x₂) = 5x₁+ 4x₂. If p₁=2.5,p₂=0.5 and m=50. Which of the following is correct?

a.The optimal bundle must be corner solution.

b.The optimal bundles include both corner solution and interior solution.

c.The optimal bundle must be interior solution.

d.None of the above.