Cell value matches value from Sheet1. Compare number from Cell2 and show difference

Hi All

I will do my best to describe what I need to achieve. If description not clear enough please shout up. We will work it through somehow

OK...

Sheet1 is Main Sheet which never will be amended and these numbers will be a source for pulling mathematical functions
See attached :
Sheet1.png
Don't be bothered about cell colors etc. They are for my reference

Sheet2
Will contain same Problem Ticket numbers but different (or same) values with number of 'Linked Incidents'
See screenshot
Sheet2.png

Based on Problem ID 10248
Main sheet shows 92 Linked Incidents
Value on Sheet two brings 93

If A5 Sheet2 value can be found in ColumnA Sheet1, look for a number in ColumnC, same ROW and compare it to C7 in Sheet2 ?
Bring up difference value, which in this case would be one

Any help appreciated ! Thanks for looking