Let us take the case of 7 pounds for $8.47 first.
7 pounds of a product costs = 8.47 dollars
Then
1 pound of the same product will cost = (8.47/7) dollars
= 1.21 dollars
Now let us take the case of 9 pounds for $11.07
9 pounds of a product costs = 11.07 dollars
Then
1 pound of the same product will cost = (11.07/9) pounds
= 1.23 dollars
So from the above deductions we can see that 9 pounds for $11.07 is a better buy than 7 pounds for $8.47. I hope the procedure is clear enough for you to understand. In future you can use this method for solving similar problems.