A student began experiment for determination of $5$-day, $20^{\circ}C$ BOD on Monday. Since the $5$th day fell on Saturday, the final DO readings were taken on next Monday. On calculation, BOD (i.e. $7$ day, $20^{\circ}C$ was found to be $150$ mg/L. What would be the $5$-day, $20^{\circ}C$ BOD (in mg/L)? Assume value of BOD rate constant $(k)$ at standard temperature of $20^{\circ}C$ as $0.23/day$ (base $e$). ___________