Abaker purchased 12 lb of wheat flour and 15 lb of rye flour for a total cost of $18.30. a second purchase at the same prices, included 15 lb of wheat flour and 10 lb of rye flour. the cost of the second purchase was $16.75. find the cost per pound of the wheat flour and the rye flour.

w - amount of wheat purchased
r - amount of rye purchased 

12w+15r=18.30 /*2
15w+10r=16.75 /*3 

24w+30r=36.60, subtract this equation from the other one
45w+30r=50.25 

21w=13.65
w=13.65/21
w=0.65 is a cost per pound for wheat flour 

From the first equation we have
r=(18.30-12w)/15
r=(18.30-12*0.65)/15
r=0.70 is a cost per pound for rye flour

It costs $0.70 per pound of wheat flour and the rye flour.