For what value of a does (1/9)^a+1 = 81^a+1 x 27^2-a?

The radius of the sphere is 10 units .what is the approximate volume of the sphere use π=3.14

For each phone call robert makes,he pays $0.10 for the first minute and $0.05 for each additional minute. what is the cost for two 5 minute calls ? a $0.60b $0.30c $0.15d $0.45 show work.

The length of time for one individual to be erved at a cafeteria is a random variable having an ex- ponential distribution with a mean of 4 minutes. what is the probability that a person will be served in less than/3 minutes on at least 4 of the next 6 days?