To find the charge per minute, we can use the information provided by the points (0, 15) and (50, 90).
The first point (0, 15) indicates that when no minutes are used (0 minutes), the charge is $15. Therefore, $15 is the flat fee.
The second point (50, 90) indicates that when 50 minutes are used, the charge is $90.
We can set up the linear equation representing the cost (C) as follows:
\[ C = F + r \cdot m \]
Where:
- \(C\) is the total cost,
- \(F\) is the flat fee,
- \(r\) is the charge per minute, and
- \(m\) is the number of minutes.
From the first point (0, 15): \[ 15 = F + r \cdot 0 \Rightarrow F = 15 \]
From the second point (50, 90): \[ 90 = 15 + r \cdot 50 \]
Now, we can solve for \(r\): \[ 90 - 15 = r \cdot 50 \] \[ 75 = r \cdot 50 \] \[ r = \frac{75}{50} = 1.5 \]
Thus, the charge per minute is $1.5. Therefore, the fee the company charges per minute is:
\[ \boxed{1.5} \]
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