<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def expand(self, percentage):
 """ Expands the box co-ordinates by given percentage on four sides. Ignores negative values. :param percentage: Percentage to expand :return: New expanded Box """

        ex_h = math.ceil(self.height * percentage / 100)
        ex_w = math.ceil(self.width * percentage / 100)

        x = max(0, self.x - ex_w)
        y = max(0, self.y - ex_h)
        x2 = self.x + self.width + ex_w
        y2 = self.y + self.height + ex_h
        return Box.from_xy(x, y, x2, y2)