To prove that the sum of two rational numbers is rational, we need to use values for \( a \) and \( c \) that are rational. A rational number is any number that can be expressed as the quotient or fraction of two integers, where the denominator is not zero.
Let's evaluate the options given:
- π: This is an irrational number.
- 3: This is a rational number (it can be expressed as \( \frac{3}{1} \)).
- \( 3-\sqrt{3} \): \( \sqrt{3} \) is irrational, so \( 3 - \sqrt{3} \) is also irrational.
- \( \frac{3}{0} \): This expression is undefined since division by zero is not allowed.
The only rational option among these is 3. Therefore, you can use 3 for \( a \) in order to apply the proof that the sum of two rational numbers is rational.