Suppose $8$ people can paint $6$ houses in $3$ hours. How many houses can $3$ people paint in $4$ hours?
So it seems that $1$ person can paint $3/4$ of a house in $3/8$ of an hour. Then this implies that $3$ people can paint $9/4$ of a house in $9/8$ of an hour. Is there any easy way to convert this to the desired result?
Or maybe we should look at the fixed ratios: $8:6:3$ versus $3:x:4$.