The problem has the equation:
f(x) = (3) ^ (x/2)
In order to get the average increase in the number of flowers being pollinated from day 4 to day 10, then we need to use the equation substituting x with 4 to 10
f(4) = 9
f(5) = 12.59
f(6) = 27
f(7) = 46.77
f(8) = 81
f(9) = 140.30
f(10) = 243
Then add all the values and divide it by 7
= 559.66 / 7
= 79.95
So the correct answer is 79.95
