Eng-Math 4(10points)

Johnson walked 4km to the west, and then he walked 7km further in the same direcion.
Taking the east as the positive direction, use a directed number to represent his final position from the start the starting point.


Mrs Li reduce her weight by 2kg in the first week, gained1/2kg in the second week, continued to gain1kg in the third week, but lost 3kg in the fourth week. Find the change of her weight.

Thank you very much!