Determine whether the data has the add-add, add-multiply, multiply-multiply, or constant-second-differences pattern. Identify the type of function that has the pattern.
$$\begin{array}{rr}
\frac{x}{2} & f(x) \\
4 & 2700 \\
6 & 2400 \\
8 & 2100 \\
10 & 1800 \\
1500
\end{array}$$