Using a linear function, we have that:
a) The costs are:
i. C(x) < $1.3.
ii. C(x) > $2.3.
b) The times are:
i. Less than 9 minutes.
ii. At least 16 minutes.
<h3>What is a linear function?</h3>
A linear function is modeled by:
y = mx + b
In which:
- m is the slope, which is the rate of change, that is, by how much y changes when x changes by 1.
- b is the y-intercept, which is the value of y when x = 0, and can also be interpreted as the initial value of the function.
In this problem, the <u>y-intercept is of 0.3, while the slope is of 0.2</u>, hence the cost for a call of x minutes is:
C(x) = 0.3 + 0.2x.
For calls shorter than 5 minutes, the costs are:
C(x) < 0.3 + 0.2 x 5
C(x) < $1.3.
For calls longer than 10 minutes, the costs are:
C(x) > 0.3 + 0.2 x 10
C(x) > $2.3.
The cost is less than $2.10 for calls of less than x minutes, found as follows:
0.3 + 0.2x < 2.1
0.2x < 1.8
x < 9.
The cost is greater or equal to $3.50 for calls of at least x minutes, found as follows:
0.3 + 0.2x >= 3.5
0.2x >= 3.2
x >= 16.
More can be learned about linear functions at brainly.com/question/24808124
#SPJ1