I will explain how 42 came.
After doing the first step, we get quotient =2
Whatever the quotient, double it(multiply it with 2)
That's how we get 4
Now use different combinations of two digit numbers with ten's digit 4 such that number multiplied with its unit place number is less than the obtained remainder.
Here we get 42*2 < 100
2 is the unit place's number
So that's how 42 came
So by trial and error method we must find units place