Which expression is equivalent to \( 9 k+9 k \) ?

When you combine like terms, \( 9k + 9k \) simplifies to \( 18k \). Think of it like having 9 apples and then getting another 9 apples; now you have a total of 18 apples! This process of combining like terms is a fundamental skill in algebra, which helps simplify expressions and equations. Remember, the more you practice with combining terms, the sharper you'll become in recognizing patterns and performing calculations quickly!