An optically active substance ‘A’ undergoes first order conversion into two another optically active compounds ‘B’

 and ‘C’ in their aqueous solutions as shown. From the data given below regarding total optical rotation given at different instant, calculate the rate constant in terms of hour^-1.
$\mathrm{A}\to \mathrm{B}+\mathrm{C}$
t(min)                                      0      10      $\infty$
Total optical rotation         10°      0°     -10°
[Given: ln 2=0.7]
[Multiply your answer with 100 and fill OMR.]