Can someone please help?

The owner of the plant nursery where you were tells you to fill 350 ml bottles from a 30 l from a fertilizer

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

Calculate the average rate of change over the interval [1, 3] for the following function. f(x)=4(5)^x a. -260 b. 260 c. 240 d. -240