A hanging mass \( M \) is connected to a four times bigger mass by using a string pulley arrangement, as shown in the figure. The bigger mass is placed on a horizontal ice-slab and being pulled by \( 2 \, Mg \) force. In this situation, tension in the string is \( \dfrac{x}{5} \, Mg \) for \( x = \) ______. Neglect mass of the string and friction of the block (bigger mass) with ice slab.
(Given \( g = \) acceleration due to gravity)
