The function \( f(x) = 1,500x + 300 \) represents Manuel's total earnings after \( x \) months, where:
- \( 1,500x \) is the amount he earns from his monthly salary for \( x \) months,
- \( 300 \) represents the hiring bonus he received.
To find out how much he received as a hiring bonus, we can look at the constant term in the function.
Thus, the hiring bonus Manuel received is $300.