Please let it be solved without the use of a calculator or calculating device

OMB, OAN and APB are all straight lines as can be seen in the figure below. AN = 20A, Mis the midpoint of OB, OA = a, OB = b and AP = KAB (where k is a scalar quantity). Given that MPN is a straight line: 27 of 28 B M a) Find AB [0.5 Mark] b) Find MN in terms of a and b [1.5 Mark] c) Find PN in terms of a , b and k [1.5 Mark] d) Find MP in terms of a , b and k [1.5 Marks]