Final answer:
Without additional data, we cannot choose a specific exponential growth model; however, to adapt an existing model to weekly data, it must be divided by 7 to find the weekly average.
Step-by-step explanation:
The first part of the question concerns identifying an exponential growth model which represents the number of text messages sent. Of the choices presented, the exact model cannot be determined without additional context. However, the question is likely pertaining to understanding the structure of an exponential function. An exponential function typically takes the form f(t) = a * e^(b(t - t0)), where a is the initial amount, e is the base of the natural logarithm, b is the growth rate, and t0 is the initial time period.
For the second part, to modify the model to represent the number of text messages sent each week instead of the current period, we should divide the model by 7 because there are 7 days in a week. This will yield the average number of text messages sent per week.