I need to solve as an equation. A coffee merchant has coffee beans that sell for $9 per pound and $12 per pound. The two types are to be mixed to create 100 lb of a mixture that will sell for $11.25 per pound. How much of each type of been should be used in the mixture?

Question

Assume 1 lb of mix contains x lb of the $9 coffee and 1-x lb of the $12 coffee.
9 x + 12 (1-x) = 11.25
0.75 = 3x
x = 0.25 (25% $9 coffee and 75% $12 coffee.