Bart company charges a lower rate. It is lower by rate $ 0.5 per hour
Solution:
Given that Ace bike rentals rents bikes for $28 per day. Renters can keep the bike for 8 hours
Also given that Bart's bikes rents bikes for $30 per day. Renters can keep the bike for 10 hours
To find: company that charges lower rate
Let us find the hourly rate of Ace and Bart

Hourly rate of Ace company:
Rental price = $28
total time in a day 8 hours

So the hourly rate of Ace company is $ 3.5 per hour
Hourly rate of Bart company:
Rental price = $ 30
total time in a day 10 hours

So the hourly rate of Bart company is $ 3 per hour
Comparing hourly rate of both companies
Ace company is $ 3.5 per hour
Bart company is $ 3 per hour
Bart company < Ace company
3 < 3.5
Thus bart company charges a lower rate
How much lower?
hourly rate of Ace company - hourly rate of Bart company = 3.5 - 3 = 0.5
So, it is lower by rate $0.5 per hour