Let \( a \) and \( b \) respectively be the points of local maximum and local minimum of the function \( f(x)=2x^{3}-3x^{2}-12x \).
If \( A \) is the total area of the region bounded by \( y=f(x) \), the \( x \)-axis and the lines \( x=a \) and \( x=b \), then \( 4A \) is equal to __________.
