What are the roots of the equation x2 - 10x + 21 = 0? A) 1 and 21
B) -5 and -5
C) 3 and 7
D) -3 and - 7

Martha is training for a duathlon, which includes biking and running. she knows that yesterday she covered a total distance of over 55.5 miles in more than than 4.5 hours of training. martha runs at a speed of 6 mph and bikes at a rate of 15.5 mph.