Is the answer 12 gallons?
You need to find out the number of gallons of pure orange. Lets it call it X.
You have 30 gallons of 30% pulp, so the total gallons of the new mixture will be x + 30.
Since you want 50 % solution, you will have .50 (x +30) as what you want for the new mixture.
To get that new mixture, you need to mix X amount of 100% orange. Since its 100% orange, you will have X(1) or 1x pure orange.
Now you want to mix that pure orange with 30 gallons or 30% pulp solution, which is 30(.30).
Now you have all you need to figure out the problem.
1x + 30(.30) = .50 (x+30)
x = 12 gallons.
I hope this right! HAHA