8.66666667 that’s your answer
8.7 you need to do the Pythagorean theorem
You were given one side length and the hypotenuse so your equation should b 18^2+x^2=20^2
B.
if it's is a right angle triangle, two of the x-coordinate of the points must be the same however with the points given, we can tell that the x coordinates are different , the two points are not vertical hence it does not form a right angle triangle.