= 139*( 100- 1)

= 139* 100- 139* 1

= 13900- 139

= 1376 1

There is another way:

139*99

=( 140- 1)*99

= 140*99-99* 1

= 13860-99

= 1376 1

I think the first method is better. I hope I can help the landlord and hope to adopt it.