To easier digest this question, we can multiply the 120 servings by 4 ounces to make it into a common unit of measurement. This way, we can compare ounces with ounces instead of ounces to servings. We then have 480 servings, and the poor caterer only has 60 ounces. We can put that into a fraction, 60/480. From here, things get slightly easier. All we have to do is make it into a fraction we can digest, which would be 1/8. We can turn that fraction into a decimal by simply dividing. We have 0.125. Since we are changing from a decimal into a percent, we have to move the decimal point two places to the right. We have out final answer of 12.5%.
