$1.$A post$-$tensioned concrete T$-$section bridge girder has a flange width of $1300$ mm$.$ The overall depth of the section is $2000$ mm$.$ The thickness of the flange and web are $150$ mm each. If the section is reinforced with prestressing cables of area, $6000$ mm$2,$ located at an effective depth of $1750$ mm$,$ determine the ultimate flexural strength of the section. Take fck $=40$ MPa and f$$pu $=1600$ MPa.