Mixing two kinds of candy the price of which was $2 and $4 per pound, ella got a 10-lb mix of candy, which cost $2.90 per pound. how many pounds of each kind of candy were used for the mix?

1. You have the following information given in the problem above:

 - Ella mixed two kinds of candy the price of which was $2 and $4 per pound.
 - Ella got a 10-lb mix of candy, which cost $2.90 per pound. 

 2. Therefore, let's call:

 x: pounds of the first kind of candy.
 y: pounds of the second kind of candy.

 3. Then, you have:

 2x+4(10-x)=(2.90)(10)

 4. When you clear x, you obtain:

 2x+40-4x=29
 -2x=29-40
 x=-11/-2
 x=5.5 pounds

 x+y=10
 y=10-x
 y=10-5.5
 y=4.5 pounds

The answer to that is 6