The force tending to lift the load (vertical force) is equal to 22.5N.
Why?
Since the boy is pulling a load (150N) with a string inclined at an angle of 30° to the horizontal, the total force will have two components (horizontal and vertical component), but we need to consider the given information about the tension of the string which is equal to 105N.
We can calculate the vertical force using the following formula:

Hence, we can see that the force tending to lift the load off the ground (vertical force) is equal to 22.5N.
Have a nice day!