Leslie used 20% of a half-gallon (64 ounces) of milk for a recipe. How many ounces of milk were left?

51.2 ounces.

Step-by-step explanation:

If its 20% of a 64 ounce half gallon, you just need to find the last 80% of the half gallon. Since you know it is 64 ounces you can divide it by 5 which gives you 12.8. 12.8 would be 20% so you just subtract 12.8 from 64 ounces which gives you 51.2.

Step 3 is wrong. It should've came out to: 3≥21x