To find the value of \( P \) when \( x = 51 \), we can substitute \( x \) into the function \( P = 0.79x + 20.86 \).
Substituting in the value of \( x \):
\[ P = 0.79(51) + 20.86 \]
Now, calculate \( 0.79(51) \):
\[ 0.79 \times 51 = 40.29 \]
Now add that result to 20.86:
\[ P = 40.29 + 20.86 = 61.15 \]
Therefore, the value of \( P \) when \( x = 51 \) is \( 61.15 \) million.