$30$ and $45$ pounds.
Work Step by Step
Step 1. Assume we need $x$ pounds of the popular candy and $y$ pounds of the less popular candy; the total amount is $x+y=75$ which gives $y=75-x$ Step 2. The total price is given by $1.6x+2.1y=1.9(75)$ Step 3. Substitute $y=75-x$ in the second equation; we have $1.6x+2.1(75-x)=1.9(75)$ and $1.6x-2.1x=(1.9-2.1)(75)$, thus $x=30$ and $y=45$ pounds.