[tex]\text{Distance } = \sqrt{ (x_2 -x_1)^2 + (y_2 - y_1)^2}[/tex]
You are given -9 and -3, which can also be written as (-9,0) and (-3,0) respectively.
Plugging those two points into the formula, you get:
[tex]\sqrt{ \left(-3 - -9\right)^2 + \left(0 - 0\right)^2}\\ \sqrt{ \left(-3 + 9\right)^2 + \left(0 + 0 \right)^2}\\\sqrt{\left( 6\right)^2 + 0}\\\sqrt{ 36 }\\ \sqrt{ 36 } \approx\boxed{ \bf{6}} [/tex]
So the distance between -9 and -3 is 6.
Remember the distance between two numbers, or points, is always going to be positive.
