Let’s assume this report is of a campaign you have previously sent.
There are 76 506 sent emails. The report shows that 0.41% (310) of your emails have hard-bounced and 2.70% (2 069) have soft-bounced. So, the remaining email addresses that have successfully received your campaign are 74 127.
The open rate percentage is calculated from the successfully reached email addresses, in this case from 74 127 email addresses. This is intentional as the user should focus on the relevant open rates for the valid email addresses.