Can someone me with this math problem

13 units

The x value goes from x = 21 to x = 9, which is an x distance of 12 units (21-9 = 12)

The y distance is 5 units (16-11 = 5)

We have a right triangle with legs of 12 and 5. The hypotenuse is x

Use the pythagorean theorem to find x

a^2 + b^2 = c^2

5^2 + 12^2 = x^2

25 + 144 = x^2

169 = x^2

x^2 = 169

x = sqrt(169)

x = 13

The hypotenuse of this right triangle is 13 units, so this is the distance between the two points.