A and B are points on j.
C and D are points on k.
Join AD and BC.
ABCD is a quadrilateral.
Clearly, the quadrilateral ABCD is the only plane that contains the points A, B, C and D.
Hence, correct answer is option A. Exactly one.
Is there a picture of the graphs?
Answer: 6 students
What we know:
Students: 24
Students who play checkers: 
Students who also play sudoku:
of the 
24 ÷ 3 = 8, so 8 × 2 = 16 (students who play checkers)
× 2 = 
So the answer is,
6 students play both checkers and sudoku
you can use the number sentence 42/7