Let for some function \( y=f(x) \), \( \int_{0}^{x} t f(t)\,dt = x^{2} f(x), \, x>0 \) and \( f(2)=3 \). Then \( f(6) \) is equal to:
\( 2 \)
\( 3 \)
\( 1 \)
\( 6 \)