math
posted by leenie .
susan wants to mix 10 pounds of virginia peanuts that cost $3.50 a pound with Spanish peanuts that cost $3.00 a pound to obtain a mixture that costs $3.40 a pound. How many pounds of Spanish peanuts should she use?

let the amount of Spanish peanuts to be added be x lb
then 3.5(10) + 3x = 3.4(10+x)
solve for x