The first $1500 is taxes at 2%, which comes out to $30. The next $3000 is taked at 3%, which comes out to $90. This leaves a remainder of $8000-($1500+$3000). That'd be $3500. Williams must pay 6% of that $3500, or $210.
His total tax bill would then be $210+$90+$30, or $330.