Question 915878
This grocer is mixing two kinds of coffee. I always love the smell of coffee! 
We will say that x sells for $2.15 per pound and y sells for $2.45 per pound.

Altogether there are 18 pounds of coffee he is selling.
The algebraic equation would be x + y = 18

At $2.30 per pound, he will make 18 * $2.30 = $ 41.40

So, how many of the x and y kinds of coffee should he use to make the $2.30 per pound mixture which will net him $41.40?
The algebraic equation would be  2.15x + 2.45y = 41.40

We now have two equations :

x+y = 18
2.15x + 2.45y = 41.40

Substituting  x= 18 -y in the second equation gives us

2.15(18-y) + 2.45y = 41.40
38.70 - 2.15y + 2.45y = 41.40
38.70 + 0.3y = 41.40
0.3y = 41.40 - 38.70
0.3y= 2.70
y=9

If y=9, then x= 9 as well. 

So, he will use 9 pounds of the $2.15 per/lb one and another 9 pounds of the $2.45per/lb one.