Let's try this problem to help us remember how to double a number.
Double $9$9.
When we add the same number more than once, we can think of it as multiplication, as we see in this video.
Write this addition as a multiplication.
$3+3+3+3$3+3+3+3
Interpret products of whole numbers, e.g. Interpret 5 × 7 as the total number of objects in 5 groups of 7 objects each.