I drew this table to make things clearer for you.
The total price is found by multiplying the Price/Weight by Weight. Now, let's analyze the table. We can see that the total price is expressed as:
But we still need another relation. Let's go back to the table. We can see that the total weight is expressed as:
But what is c and d?
Remember, they gave you the price/weight for dried fruits:
Can you work your way from here?
Try to write the total weight expression in terms of a and b. Then it only becomes a matter of simple substitution.