answer the following A and B

Sigma Computer Company must purchase 600 customized hard drives for its laptop computer for next year. As shown below, the company received quotes from three vendors for these drives: For example, Champion will require a fixed cost of $10,000 to tool up to make the drives. It will charge \$265/unit for the first 250 units and $190 /unit for additional units up to a maximum (supplied at both prices) of 800 units. a. Formulate Sigma's vendor selection problem as an MIP model and optimize it using a spreadsheet optimizer. b. Reformulate and reoptimize the model of part (a) under the additional constraint that no vendor is allowed to supply more than 75% of the total number of units required