Answer:
A = 4, B = 3, C = 7, D = 6
Step-by-step explanation:
A = 4 because A represents the number of people who didn't visit either place. This means that B + C + D = 20 - 4 = 16. To find C, which is the overlap we can do 10 + 13 - 16 = 7 so C = 7 which means B = 10 - 7 = 3 and D = 13 - 7 = 6.
You multiply 5 times 10, which gives you 50. This is the length of one side. Since it's a square, all sides are the same length.
Answer: 50cm x 50cm
All the components in the state vector need to sum to 1. You're given that component corresponding to state 1 is 0.2, and that the component for state 3 is 0.
That leaves states 2 and 4, for which you're told that the component for state 2 is four times as large. If

is the component for state

, then you have

which means

. So the state vector is

.