Let a_1, a_2, a_3, … be a G.P. of increasing positive terms such that a_2. a_3. a_4=64 and a_1+ a_3+ a_5=813/7. Then a_3+ a_5+ a_7 is equal to:

Let $\displaystyle \mathrm{a}_1, \mathrm{a}_2, \mathrm{a}_3, \ldots$ be a G.P. of increasing positive terms such that $\displaystyle \mathrm{a}_2 . \mathrm{a}_3 . \mathrm{a}_4=64$ and $\displaystyle \mathrm{a}_1+\mathrm{a}_3+\mathrm{a}_5=\frac{813}{7}$. Then $\displaystyle \mathrm{a}_3+\mathrm{a}_5+\mathrm{a}_7$ is equal to :