Please Help Find the indicated side of the right triangle

Two line segments are shown in the figure below. suppose that the length of the line along the x-axis is 6, and the length of the hypotenuse of the triangle is 10. what is the equation of the hypotenuse line (shown in red, below)?

Find the distance between (7,-6) and (-3,-9)

How can you find the magnitude of a vector, v = < x,y > , where the horizontal change is x and the vertical change is y?