Let's break down the problem step-by-step:

1. Given Function: We start with $f(x) = -3x$.

2. Reflection Line: The reflection line is $y = 0$, which is the x-axis.

3. Reflection of $f(x)$ Along the x-axis:

   • When we reflect $f(x) = -3x$ across the x-axis, we change the sign of $f(x)$.
   • The reflection of $f(x) = -3x$ across $y = 0$ is $h(x) = 3x$.

4. Writing $h(x)$ in the Given Form:

   • We want $h(x)$ in the form $h(x) = px^2 + k$.
   • Since $h(x) = 3x$ is a linear function, $p = 0$ and $h(x)$ simplifies to a constant term, $h(x) = 3x$.

Final Answer: [ h(x) = 3x