Need asap plz < 3✨ answer the question thx : )

What is the common difference in the following arithmetic sequence 7,3,-1,-5

On the first of each month, shelly runs a 5k race. she keeps track of her times to track her progress. her time in minutes is recorded in the table: jan 40.55 july 35.38 feb 41.51 aug 37.48 mar 42.01 sept 40.87 apr 38.76 oct 48.32 may 36.32 nov 41.59 june 34.28 dec 42.71 determine the difference between the mean of the data, including the outlier and excluding the outlier. round to the hundredths place. 39.98 39.22 0.76 1.21

F(n + 1) = f(n) – 8. if f(1) = 100, what is f(6)?