To find the number of chirps per minute (N) using Dolbear’s law given that the temperature (T) is 59°F, we start with the formula:
\[ T = 50 + \frac{N - 40}{4} \]
Substituting \(T = 59\) into the equation:
\[ 59 = 50 + \frac{N - 40}{4} \]
Now, we can solve for \(N\):
- Subtract 50 from both sides:
\[ 59 - 50 = \frac{N - 40}{4} \]
\[ 9 = \frac{N - 40}{4} \]
- Multiply both sides by 4 to eliminate the fraction:
\[ 9 \times 4 = N - 40 \]
\[ 36 = N - 40 \]
- Add 40 to both sides:
\[ 36 + 40 = N \]
\[ N = 76 \]
Thus, the number of chirps per minute (N) is 76.