multi derviative?

Question

approximately 40 – 8x + 5y consumers will buy the first type and 50 + 9x -7y will buy the second type. If the cost of manufacturing the first type is $1,000 per system and the cost of manufacturing the second type is $3,000 per system, how should the telephone company price the systems to generate maximum profit?

Answer 1

find second derivative of each, find zero's and test to see whether they are maximum or minimum... you want maximum in this case... then substitute the info u know