Answer: 27 Pounds
Explanation:
x = the weight of the chocolate candies used
the value of 20 pounds of peanuts + the value for x pounds of chocolate candies = the value of the mixture
4.50*20 + 2.25*x = (20 + x)*3.20
by solving this equations we find
x = 27.37 = 27 pounds (rounded to the nearest pound)
they should use 27 pounds of chocolate candies.