Find two numbers whose product is 42 and difference is 1.

Okay, So We Need Two Numbers That Multiply To Get 42. Lets Look At All Of The Ways To Get 42.
1 * 42 
2 * 21
6 * 7
7 * 6 
21 * 2
42 * 1

So, 21 and 2 don't have a difference of one. 
42 and 1 don't have a difference of one. 

6 and 7 have a difference of one, which means your two mystery numbers are 6 and 7.

This is the answer for your problem you need to subtract