We know, 3 feet = 1 yard.
We have to convert feet to yards to calculate the ratio so that the final answer doesn't have any unit.
Therefore, 21 feet = [tex]\frac{21 feet}{3 feet}yards[/tex] = 7 yards
Thus, the ratio
[tex]\frac{21feet}{8yards} =\frac{7yards}{8yards} =\frac{7}{8}[/tex]
The fraction [tex]\frac{7}{8}[/tex] is already in its simplest form.
Therefore, the given ratio as a fraction in the simplest form without any units is [tex]\frac{7}{8}[/tex]