Answer:
 the number of pounds that should be mixed is 30 pounds 
Explanation:
The computation of the number of pounds that must be mixed is shown below:
Let us assume the number of pounds be x
Now the equation is 
(x) (1) + (15) (1.60) = (x + 15) (1.20)
x + 24 = 1.20x + 18
24 - 18 = 1.20x - x
6 = 0.20x
 x = 30 pounds 
Hence, the number of pounds that should be mixed is 30 pounds