Question 707780
d=rt
d=60t to Dallas.
d=45(21-t) from Dallas.
60t=45(21-t)
60t=945-45t
60t+45t=945
105t=945
t=945/105
t=9 hours for the trip to Dallas.
21-9=12 hours from Dallas.
Proof:
60*9=45*12
540=540