Produce a straight line where Y lies on AB, Z lies on DC, and YXZ//AD//BC.
CM = 3DM, hence
CM = 0.75*DC = 0.75*AB

hence
AB / CM
= AB / 0.75AB
= 4/3
= AX / CX
= BX / MX

triangle AYX similiar to CZX (AAA), therefore
AY / CZ = AX / CZ = 4/3
Therefore CZ = BY = (3/7)*AB

area of triangle BXC = BC*BY/2
= BC*(3/7*AB)*1/2
= (BC)(AB)(3/14)
area of rectangle ABCD = (BC)(AB)
Hence, the ratio concerned
= 3:14