Answer:
Screen 1: 200, Screen 2: 125 , Screen 3: 175
Explanation:
Screen 1 
Multiply 40% and 500 
Convert 40% to a decimal 
40/100=0.40
500*0.40
200
Screen 2 
Multiply 25% and 500 
Convert 25% to a decimal 
25/100=0.25
500*0.25
125 
Screen 3
Subtract the amount of people that went to screens 1 and 2 from the total 
500-200-125
175 
So, Screen 1 had 200 visitors, 2 had 125 and 3 had 175 
Hope this helps! :)