emily drove 3/7 of the total distance and holly drove the rest which explains that holly drove 4/7 of the whole distance.
if 4 parts of the distance equals 24 miles, then 1 part would be 24/4 is 6.
since emily drove 3 parts of the whole distance, it is 6 × 3 = 18 miles.
travelling time of emily = 18/45 = 0.4 hr
travelling time of holly = 24/54 = 0.4 hr
--> total traveling time = 0.8 hr
i hope it is right