Before we solve anything, we need to know how many cups there are in a gallon.
There are 16 cups in 1 gallon.
We have 1.5 gallons.
There is a shortcut to finding the 0.5 extra gallons;
Divide the amount of cups per gallon by 2. This will give us an equivalent of 0.5 gallons.
16 / 2 = 8.
There are 8 cups per 0.5gal.
Now that we have our gallons translated into cups, let's sum up.
16 + 8 = 24.
There are 24 cups in 1.5 gallons.
The chef can get 24 1-cup servings out of the pot.
I hope this helps!