Finding Number of Red Marbles

Alice has a collection of marbles. She has twice as many red marbles as blue marbles. If she has 12 blue marbles, how many red marbles does Alice have?

To find the number of red marbles, you can set up the equation:

Let the number of blue marbles be represented by $b$. Therefore, the number of red marbles can be represented as $r = 2b$.

Given that $b = 12$, substitute this value into the equation to find $r$.