The function \( f(x) = 1,500x + 300 \) represents Manuel's total earnings after \( x \) months, where:
- \( 1,500x \) represents his total salary over \( x \) months (with \( 1,500 \) being the monthly salary),
- \( 300 \) represents the hiring bonus he received.
To determine how much Manuel received as a hiring bonus, we can identify the constant term in the function.
Thus, the hiring bonus is:
\[ \text{Hiring Bonus} = 300 \]
So, Manuel received $300 as a hiring bonus.