Can you post the comments from an Approval Process into the chatter feed when an item is approved?

I am trying to update a record field with type formula. Below is the formula that I have written. Any help?

List<[Order_Item__c> Orders = [SELECT Product_Record_Type__c, Total_Price__c FROM [Order_Item__c]];
Integer total = 0;

for ([Order_Item__c] order : Orders){

IF(order.Product_Record_Type__c == "Building Option",
total += order.Total_Price__c;
)

};

return total;

Can you post the comments from an Approval Process into the chatter feed when an item is approved?

I am trying to update a record field with type formula. Below is the formula that I have written. Any help?

List<[Order_Item__c> Orders = [SELECT Product_Record_Type__c, Total_Price__c FROM [Order_Item__c]];
Integer total = 0;

for ([Order_Item__c] order : Orders){

IF(order.Product_Record_Type__c == "Building Option",
total += order.Total_Price__c;
)

};

return total;