What is the radius of a circle whose area is equal to the sum of the areas of two circles whose radii are 20cm & 21cm?

What are the values of m∠abc, m∠cbf, m∠abd and m∠dbe in the given figure? explain or show your work?

Acertain population of bacteria demonstrates exponential growth doubles in size every 4 days. how long will it take the population to triple in size?

Fa bus driver leaves her first stop by 7: 00 a.m., her route will take less than 37 minutes. if she leaves after 7: 00 a.m., she estimates that the same route will take no less than 42 minutes. which inequality represents the time it takes to drive the route, r?