Question 4
What are the two pulleys in activity 1 for?
The right answer is the one marked above.
To turn the direction of the force. That lets the two balances stay out to the side while both pulls still reach the trolley along one line in one direction.
A smooth pulley does not change the size of the force — if it increased it, the activity's own conclusion would collapse. Nor does a pulley change the trolley's mass.