A multiple regression model has the form = 12 – 4 x1 + 5 x2. As x1 increases by 7 units (holding x2 constant), is expected to (enter increase, decrease) by units. A multiple regression model has the form = 12 – 4 x1 + 5 x2. As x1 increases by 7 units (holding x2 constant), is expected to (enter increase, decrease) by units.