What must be a factor of the polynomial function f(x) graphed on the coordinate plane below?

On a coordinate plane, a parabola opens up. It goes through (0, 3), has a vertex at (3.5, 3), and goes through (6, 0).
x – 3
x – 1
x + 1
x + 3

Luke started a weight-loss program. the first week, he lost x pounds. the second week, he lost pounds less than times the pounds he lost the first week. the third week, he lost 1 pound more than of the pounds he lost the first week. liam started a weight-loss program when luke did. the first week, he lost 1 pound less than times the pounds luke lost the first week. the second week, he lost 4 pounds less than times the pounds luke lost the first week. the third week, he lost pound more than times the pounds luke lost the first week.