Grace arrived at the bus station at $8:10$, and the trip was $1$ hour long, so she departed at $7:10$. 
Grace was going to meet her friends at the bus station. Right now, it is $8:40$. Grace arrived at the bus station half an hour ago. The trip from her home to the station was $1$ hour long. What time did Grace depart toward the bus station? 
Options:
(a) $7:20$ 
(b) $7:10$ 
(c) $7:50$ 
(d) $8:10$ 