"5/6 of 30" is the same thing as 5/6 times 30.
To multiply fractions, the numerator and denominator of each fraction is multiplied, and then simplified.
So:
\(\frac{5}{6} \times 30\) =
\(\frac{5}{6} \times \frac{30}{1}\) =
\(\frac{5\times 30}{6 \times 1}\) =
\(\frac{150}{6}\) = 25