56 84 ? 189 283.5 425.25

but vipin,why to make it so complicated when it can be done so easily i.e., just by multiplying 1.5 to the previous number.........

X,X+X/2,.........this is the series or U can say X, 3/2X,9/4X......next element is the sum of previous element and its half

sorry it is 126

the answer is 125.each number here is multiplied by 1.5.