Answer:
10 units. Read more for why!
Explanation:
When an object is translated (moved) in a specific direction, the lengths of its sides remain unchanged.
Soo..
Only the position of the object changes. So, if the original rectangle has a side that is 10 units long, after it's translated down 4 units and to the right 5 units, that side will still be 10 units long.
you are not changing its shape or size. Therefore, the length of the side will remain 10 units even after the translation.