Answer:
n(B) = 26.
Explanation:
n(A U B) = 70 means there are a total number of elements in the 2 sets A and B.
n(AnB) = 25 means that 25 of the 70 elements are in Both sets A and Set B.
n(A - B) = 18 means the difference in number of elements in A and B is 18.
So we have
a - b = 18
a + b = 70 where a and b are the number of elements in and A and B. ( i. e. in n(A) and n(B) )
Adding the 2 equations
2a = 88
a = 44
and b = 70 - 44
= 26.