In the arrangement shown in the figure, find the acceleration of M in upward direction. The pulleys are light. The strings are mass less and friction between the string and the pulleys is negligible. The options are given. The final answer is (B) and this was the solution: I don't understand the 1+7x2 step right there. Also I fail to understand why there is 49m in the denominator of the solution instead of 7m (I'm assuming the equation is multiplied by 7. I might be wrong though.) Can anyone explain me the solutions please? Thanks. P.S.: Sorry about the low quality images, it was in a kind of jiffy.