Anyone please help me?

What is the measure of ac? 5 units 13 units 26 units 39 units 3x- 2b 6x + 9

Cody started biking to the park traveling 15 mph, after some time the bike got a flat so cody walked the rest of the way, traveling 4 mph. if the total trip to the park took 6 hours and it was 46 miles away, how long did cody travel at each speed? solve using rate times time= distance

1) prove that 731^3−631^3 is divisible by 100 2) prove that 99^3−74^3 is divisible by 25