The given product p × q = 2430 …(i)

The last digit is 0, so one two of the digits must be 5 and other one an even number 2, 4, 6 or 8.
Let this unknown digit be x.

So, p = 10x + 5 and q = 50 + x
putting in (i),
(10x + 5) × (50 + x) = 2430
Now, try 2, 4, 6 and 8,
x = 4 (we can easily eliminate others as they will yield either too big or small number than 2430)

Therefore, p = 45 and q = 54
Required difference = q – p = 54 – 45 = 9