Step-by-step explanation:
Divide 140 by [tex]2\frac{4}{5}[/tex] to represent the amount of hours he worked.
To make dividing easier, [tex]2\frac{4}{5}[/tex] can also represent 2.8 as a decimal.
[tex]\frac{140}{2.8} =50[/tex]
He has worked 50 hours after completing 140 rows of grapes.