What's the answer and how do you do this?

the rate for the first 3 minutes is a, since it's a flat-fixed value, thus the cost will be a.

for Jackson, t > 3, namely 4 and higher, if he's on the phone longer than 3 minutes say hmmm 4 minutes, the the last minute is at a rate r, and his cost will be 3a + r1. now let's check a table.

4 minutea + r13a + r(4 - 3)

5 minutesa + r23a + r(5 - 3)

6 minutesa + r33a + r(6 - 3)

t minutesa + r(t-3).

1 number

if we use a graphing calculator, there is only one such number that satisfies the conclusion of the mean value theorem, that is, a number such that

where the right-hand side is the average rate of change of f on the interval [0.5,0.75], which is the slope of the secant line.

in the attached graph, the black line is the secant line which has its slope as the average rate of change of f on [0.5,0.75], while the orange line is the only tangent line to the graph of f in the interval that satisfies the mvt conclusion.

570, the answer is 570, hope it