Question about Common App transcripts when having transferred schools

My son attended two high schools. His former school was a large, public school where he achieved high grades. His transcript there was a cumulative weighted average of 4.12.

His second and current school is a small private and even more rigorous. There he has a cumulative unweighted gpa of 3.31.

Now he is filling out the Common Application. The question is what does he put for his GPA. Should we do the math and combine it ? That would be a 3.5 if I did it correctly. Should he leave it blank and let the schools figure it out in the two seperate contexts? This is a very important part of the Common App. so we don’t want to make any mistakes! I know the admissions people will analyze it but it seems a tad detrimental to put his current average on there as his school is so much more challenging than the first one, which is also considered a very top public high school.
thanks for any insight!

@GivemeChocolate what did you end up doing? We are in a similar situation.