Jill measured the length of her eraser she wrote 5 on her paper without the unit. which metric unit should Jill include?

Depends, did you assume that jill is a human?

if jill is a human then probbly 5 centimeters or cm

if jill is a giant, then 5m or km depending on the type of giant she is

if jill is an ant or fairy then probbably 5mm