Grace arrived at the bus station at $7:50$, and the trip was $1$ hour long, so she departed at $6:50$. 
Grace was going to meet her friends at the bus station. Right now, it is $8:20$. 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: $6:50$ 
c: $7:50$ 
d: $8:50$ 