A store is having a sale on jelly beans and trail mix. For 3 pounds of jelly beans and 5 pounds of trail mix, the total cost is $17 . For 9 pounds of jelly beans and 7 pounds of trail mix, the total cost is $37 . Find the cost for each pound of jelly beans and each pound of trail mix.

Set up your two equations: 
9x+7y=53 
3x+5y=25 
X=cost per pound of jelly bean 
Y=cost per pound of trail mix 
Multiply the second equation by (-3): 
-9x-15y=-75 
+ 9x+7y=53 <---- copy first equation and add them 
—————— 
0x-8y=-22 
Then solve for y: 
Y=2.76 this is your cost per pound of trail mix. 
Then plug y back in to one of the original equations and solve for x: 
3x+7(2.75)=25 
X=3.75 this is you cost per pound of jelly beans