Three(two squared minus9)

Iwant to know what 3g+5h+4g-2h is my teacher is too selfish to tell us

Answer for 10 points show work you guys in advanced < 3

Every weekday, mr. jones bikes from his home to his job. sometimes he rides along two roads, the long route that is shown by the solid lines. other times, he takes the shortcut shown by the dashed line. how many fewer kilometers does mr. jones bike when he takes the shortcut instead of the long route?