Answer: 13
Step-by-step explanation:
See attached graph.
A third point (18,20) may be added to the two given points to form a right triangle with sides 5 and 12. The distance, x, between the original two points is given by x^2 = 5^2 + 12^2
x^2 = 25 + 144
X^2 = 169
x = 13
