Rational simply means they can be written as a fraction.
In this example 6 - 10 are two rational numbers that equal -4
Here they are in rational form:
\(\frac{6}{1} - \frac{10}{1} = \frac{-4}{1}\)
I could even write them like this:
\(\frac{18}{3} - \frac{20}{2} = \frac{-4}{1} = -4\)
