3 children tuuging rubber tube ,one exert force of 40 N[N 30 E] , another force of 30 N[W], and a third a force of 50 N[S 45 W].
What is the net horizontal force on the tube?

Assuming by "horizontal" you mean "east-west," to calculate this you add up the horizontal component of each of the three forces. It's easiest to call the east as zero degrees, north as 90, west as 180 and south as 270 degrees. For example, the first force is 40 Newtons in a direction that is 30 degrees east of north, so its horizontal component is 40*cos(60) = +20 N. The second force is 30 N to the west, or -30 N. Now, can you determine the horizontal component of the third force, and then add them together?