We are given the following fractions:
[tex]\frac{25}{30}-\frac{21}{30}[/tex]To subtract fractions with the same denominator, in this case, 30, we leave the same denominator and operate the numerators, like this:
[tex]\frac{25}{30}-\frac{21}{30}=\frac{25-21}{30}=\frac{4}{30}[/tex]Now we simplify the fraction by dividing both parts by 2:
[tex]\frac{4}{30}=\frac{\frac{4}{2}}{\frac{30}{2}}=\frac{2}{15}[/tex]