Hello i was trying to get the understanding on how is 4-6+6= answer (4-6=2+6=8) but me being in high school i know its not that so someone break it down

Atutoring service offers a free one-hour tutoring session. after a client signs up, the next 10 hours of tutoring are billed at a rate of $30 per hour. for all the hours after that, the client receives a discounted rate. if a client pays $664 for 25 hours of tutoring, what is the service's discounted hourly rate? a) $24.50 b) $25.54 c) $26.00 d) $26.56