Hi,
To do that, you can use IF function in the Nested IF form as follows:
=IF(A1>75,A1,IF(A1<=75,A1+25))
If you have Excel 2019 or Office 365 installed in your machine, you can use IFS function which is the simplified version of Nested IF.
=IFS(A1>75,A1,A1<=75,A1+25)
Hope that helps