Vimla starts for office every day at $9 \; \text{am}$ and reaches exactly on time if she drives at her usual speed of $40 \; \text{km/hr}.$ She is late by $6 \; \text{minutes}$ if she drives at $35 \; \text{km/hr}.$ One day, she covers two-thirds of her distance to office in one-thirds of her usual time to reach office, and then stops for $8 \; \text{minutes}.$ The speed, in $\text{km/hr},$ at which she should drive the remaining distance to reach office exactly on time is
- $29$
- $27$
- $28$
- $26$