C) Tom did not distribute to both terms in parentheses.
Step-by-step explanation:
Addition within a paranthesis has a distributive property to the multiplier outside the paranthesis. Ignoring this will lead to a wrong value for the operation.
The correct answer is "rational" . It is not an "integer" because it is a "decimal value". It is not "irrational" because the decimal value terminates and does not repeat.