Proof that this question is not mathematically solvable unless it is a riddle
Take any number, say "x". In the expression y=x  y could be either odd or even. To make it even, we change the expression to y=2x.
Here, y is an even number since y=2x and every even number is a multiple of 2 and every multiple of 2 is an even number.
Even here, only y is an even number. "x" could might as well be an odd number. But even if so, a perfect double or a multiple of 2 is always an even number.
Then, if the expression y=2x is an even number indeed, then the expressiony=2x+1 or y=2x-1 will be odd since every even number is succeeded and preceded by an odd number. Since 30-1 or 30+1 are not even, or  will never be 30.