My math teacher didn't explain how to do this stuff and I've been struggling to understand what it is for like the past half hour. Please help. (sorry its a PDF there was no other easy way)

Atruck can be rented from company a $50 a day plus $0.60 per mile. company b charges $20 a day plus $0.80 per mile to rent the same truck. find the number of miles in a day at which the rental costs for company a and company b are the same