The diagram below shows a Sudoku puzzle with a difference. Some of the lines between adjacent cells have a number on them; this is the product of the numbers in the cells. The normal rules of Sudoku also apply: the numbers 1 to 9 must appear once each in each row, once in each column, and once in each square block.
Can you solve this puzzle?

The answer would be: b

So the first thing we do is to multiply the top equation by 3. the reason i want to do this is i notice there will be a 6y on both equations and can possibly add/subtract them. so we get 6y = -3x + 27. adding that and the second equation we get 6x = 27-15 which is 12. divide by 6 and we get 2. ∴ x = 2. substituting 2 into the first equation we get 2y = -2 + 9 which is 7. divide by 2 and we get 7/2. ∴ y = 7/2, x = 2.