Using a linear function, it is found that Sarah can use 3.7 gigabytes while staying within her budget.
A linear function is modeled by:
y = mx + b
In which:
Considering the flat cost as the y-intercept and the cost per gigabyte as the slope, the cost of using g gigabytes is:
C(g) = 4g + 69.
She wants to keep her bill at $83.80 per month, hence:
C(g) = 83.80
4g + 69 = 83.80
4g = 14.80
g = 14.80/4
g = 3.7.
Sarah can use 3.7 gigabytes while staying within her budget.
More can be learned about linear functions at https://brainly.com/question/24808124
#SPJ1