What is this? may I ask? did you mean to attach a photo?
Problem: 6|-3|-4|5|
Whenever something is in: |21| in the lines, you would just count the number itself.
So it is: 6·3-4·5 which would equal: 6·3-4·5
The answer to 6·3 is 18, so its 18 minus the answer of 5·4 which is 20.
So its: 18-20= -2
~Hope i helped. :)
