(section 3. 4. ) find the optimal order, and its cost, for evaluating the product a1 x a2 x a3 x a4 x a5, where
a1 is (10 x 4)
a2 is (4 x 5)
a3 is (5 x 20)
a4 is (20 x 2)
a5 is (2x50)