The average heartbeat rate for persons 12 to 16 years old is 80 beats per minute at rest. at this rate how many times does the heart beat in two and a half hours?

Problem number 26 of the rhind papyrus says: find a quantity such that when it is added to of itself the result is a 15. the modern day equation that models this problem is x + x = 15. what is the solution to the equation? x = 10 x = 12 x = 15 x = 30