My dad has 4 oak and maple boards from the lumber yard. each oak board is 3 centimeters thick. each maple board is 4 centimeters thick. when my dad stacks the boards, the stack is 15 centimeters thick. how many of each type of board does he have?
oak boards
maple boards

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?