Let's use the variable x to represent the number of pounds of arbequina olives and y to represent the number of pounds of green olives.
The final blend will have 9 pounds, so we have:
And the final price is $20 per pound, so we have:
From the first equation, we have y = 9 - x. Using this value of y in the second equation, we have:
Therefore she needs 5 pounds of arbequina olives and 4 pounds of green olives.