To answer this you will find the total amount of sunblock that can be filled in 10 hours. Then we will convert the number of ounces to gallons.
1. 150 bottles per hour for 10 hours is 150 x 10.
1500 bottle can be filled.
2. 1500 bottles at 20 ounces per bottle is 1500 x 20
30000 ounces of sunblock
3. There are 128 fluid ounces in each gallon so take 30000 ounces and break it into groups of 128 ounces.
30000/128 = 234.375 gallons
You will need at least 235 gallons of sunblock.