Multiplication looks at equally sized groups. Doubling means multiplying equally sized groups by $2$2. Can you solve this problem?
$9\times2$9×2
4 groups is twice (two times) as many as 2 groups. Let's look at how to multiply numbers by 4.
$4\times4$4×4
To solve questions with $4$4 times tables, you can use the Double, Double strategy. That means you double the number, then double the answer.