Answer:
Question 1:
Of the 37 children that can't swim, 11 are in Year 4.
Therefore, 26 children in Year 4 can swim.
Question 2:
There are 21 children in Year 5 who can swim.
In Year 6, there are 30 children, 18 of which can swim.
Therefore, a total of 21 + 18 = 39 children who can swim.