A box of mass 8 kg is on a rough plane inclined at 5° to the horizontal. A force of magnitude \(P\) N acts on the box in a direction upwards and parallel to a line of greatest slope of the plane. When \(P = 7X\) the box moves up the line of greatest slope with acceleration 0.15 m/s² and when \(P = 8X\) the box moves up the line of greatest slope with acceleration 1.15 m/s². Find the value of \(X\) and the coefficient of friction between the box and the plane.