The answer is C, -6, -√225, 4 7/8.
Rational means that the number can be expressed as a fraction and integer numerators and denominators. -6 and 4 7/8 can clearly be expressed as a fraction. -6 can be expressed as -6/1 and 4 7/8 can be expressed as 39/8.
-√225 is equivalent to -15, which is rational.
A is wrong because the number includes Pi.
B is wrong because -3.0541 never ends and √99 is irrational.
D is wrong because √21 is also irrational.
