How to compare values within a table - SQL

MyTable

id year month amount

1    1999    3      10
1    1999    4      10
1    1999    5      10
2    1999    3      10
2    1999    4      25
3    1999    3      10
3    1999    5      10

How to list out the IDs when (the amount of month 3 - the amount of month 4) > 50%?

With the above data, I want to have the following output:

   id
   ==
   2
   3

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Best regards, Received on Sat Jun 26 1999 - 11:39:11 CDT