Let $$\root 3 \of a = \root 3 \of {26} + \root 3 \of 7 + \root 3 \of {63} $$     then

$$\eqalign{ & \root 3 \of a = \root 3 \of {26} + \root 3 \of 7 + \root 3 \of {63} \cr & {\text{Take round figure}} \cr & \Rightarrow \root 3 \of a < \root 3 \of {27} + \root 3 \of 8 + \root 3 \of {64} \cr & \Rightarrow \root 3 \of a < 3 + 2 + 4 \cr & \Rightarrow \root 3 \of a < 9 \cr & \Rightarrow a < {9^3} \cr & \Rightarrow a < 729 \cr & {\text{Option A is answer}} \cr} $$