F.1 Maths~~~Equation

Let present age of Tom = x
Then present age of John = x + 4.
The age of Tom two years ago = x - 2
The age of John two years ago= (x + 4) - 2 = x + 2.
2(x - 2) - (x + 2) = 9
2x - 4 - x - 2 = 9
2x=15
x = 9 + 2 + 4 = 15
∴The current age of Tom is 15

P.S. You may draw a table on rough work to make it clearer

Let current age of Tom = x
So current age of John = x + 4.
Two years ago, age of Tom = x - 2
Two years ago, age of John = (x + 4) - 2 = x + 2.
Since age of John 2 years ago is less than 2 times Tom's age by 9, that is
2(x - 2) - (x + 2) = 9
2x - 4 - x - 2 = 9
x = 9 + 2 + 4 = 15 = current age of Tom.