Since the total amount of kids who participated in the survey is 150, 100% of the pie is equal to 150 kids.
We know that 46% of the 150 kids like video games so the number of kids that like video games is 0.46 * 150 = 69.
Similarly, 14 + 16 = 30% of 150 kids like reading and art so the number of kids that like reading and art is 0.3 * 150 = 45.
Your second question is quite hard to understand. But you know that 120 kids like video games and those kids make up 40% of the total so mathematically you can say,
40% * number of total students = 120
number of total students = 120/40% = 300