You're finding a "unit rate" here: acres per hour, or acres/hour.
Divide 1/6 acre by 1/4 hour. I noticed right away that multiplying "1/4 hour" by 4 results in 1. So, I multiplied both sides of this rate by 4, obtaining
4/6 acre per 1 hour, or 2/3 acre per hour, or 2/3 acre/hr.
