To make a prediction for the hourly pay of a 25-year-old using the line of best fit \( y = 0.9x - 4.5 \), we substitute \( x = 25 \) into the equation.
\[ y = 0.9(25) - 4.5 \]
Calculating this:
\[ y = 22.5 - 4.5 \]
\[ y = 18 \]
Based on the line of best fit, the best prediction for the hourly pay of a 25-year-old is $18.00.