Peanuts cost $4/pound.
Cashews cost $9/pound.
Pecans cost $5.50/pound.
The final mixture cost is the amount of each nut by the cost of them by pound.

The mixture cost $24.75
Then, by pound, we have to sum all the pounds:
3 + 0.5 + 1.5 = 5 pounds

The final result is $4.95 by pound.