A fabric firm has received an order for cloth specified to contain at least 45 pounds of cotton and 25 pounds of silk. The cloth can be woven out of any suitable mix of two yarns A and B. They contain the proportions of cotton and silk (by weight) as shown in the following table:

__________ Cotton _________Silk

A ................30%...............50%

B ................60%...............10%

Material A costs $3 per pound, and B costs $2 per pound. What quantities (pounds) of A and B yarns should be used to minimize the cost of this order?