If x and y are integers, what is the smallest possible positive value of 30x + 18y?
Since the value of 30x + 18y must be positive, x=0 and y=0 (which gives an answer of 0) won't fit the criterion.
Although the answer must be positive, the values of x and y don't have to be positive -- one or both could be negative.
Since 30x + 18y can be factored into 6(5x + 3y), the answer must be divisible by 6.
The smallest positive integer divisible by 6 is 6; so the smallest possible answer is 6.
You can get 6 various ways; one way is to have x = 2 and y = -3.