(my decimal delimiter is the comma)
Option 1 (complex & inefficient), in A7:
="ABC"&TEXT(MAX(VALUE(SUBSTITUTE(A2:A5,"ABC",))),"###.00")
NB: you might have to validate it with Ctrl+Shift+Enter
Option 2 (more efficient):
- In your column J, only keep the SUM part of your current formula, i.e. in J4: =SUM(F4-G4)
- Select cells in column J > Format cells > Number > Custom: "ABC"###.00,"ABC"-###.00,"ABC"0.00
Then use a regular MAX formula, i.e.: =MAX(J4:J104)