If y varies directly as x, and y is 400 when x is rand y is r when x is 4 what is the numeric constant of variation in this relation?

Just tell me how to set up the equation.

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)?

In which direction does the left side of the graph of this function point? f(x) = 3x3 - x2 + 4x - 2