2gallons for 3.88,a gallon for 1.95 which is the higher unit rate

Evaluate the expression for the given value of the variable 2×(c2-5) for c=4

The random variable x is the number of occurrences of an event over an interval of ten minutes. it can be assumed that the probability of an occurrence is the same in any two-time periods of an equal length. it is known that the mean number of occurrences in ten minutes is 5.3. the appropriate probability distribution for the random variable

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