To find \( f(10) \) using the function rule \( f(x) = 3x^2 \), we can substitute \( x \) with 10.
\[ f(10) = 3(10)^2 \]
Calculating the square of 10:
\[ (10)^2 = 100 \]
Now, substituting that back into the function:
\[ f(10) = 3 \times 100 = 300 \]
Thus,
\[ f(10) = 300 \]