160
When you double both the length and width, you are multiplying by 2 twice. Whatever you do to one side of an equation, you have to repeat on the other.
l * w = 40; This is the original equation.
2l * 2w = 40 * 2 * 2; This is when you double the length and the width.
The 2 * 2 on the end can be simplified.
2l * 2w = 40 * 4
Now, simplify 40 * 4.
2l * 2w = 160
So, when you double both the length and the width, you multiply the area by 4, making the area 160.
