Please help I have been stuck for a while

Find the constant of variation for the relation and use it to write an equation for the statement. then solve the equation.

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

Find the center of the circle that can be circumscribed about efg with e(4,4) f(4,2) g(8,2)