This is going to be not that straight-forward. Assuming there is just one part on the report and your data is grouped by part, create something like the following formulas:

{@FirstAmount}
WhileReadingRecords;
Numbervar firstAmt;
BooleanVar firstIsSet;
if OnFirstRecord then firstAmt = 0;
if OnFirstRecord then firstIsSet = false;
if not firstIsSet and {TxnHist.Type} = 'C' then
{
firstAmt := {TxnHist.Amount};
firstIsSet := true;
};

{@LastAmount}
WhileReadingRecords;
EvaluateAfter({@FirstAmount});
NumberVar lastAmount;
BooleanVar firstIsSet;
if firstIsSet and {txnHist.Type = 'C'} then lastAmount := {TxnHist.Amount};

NOTE: {@FirstAmount} will set the value of the "firstAmount" variable only for the first record with a type of "C". {@LastAmount} will set the value of the "lastAmount" variable for every record of type "C" after firstAmount is set - this is the best way to get the last value.

Put both of these formulas in the details section where you are showing the data from TxnHist. Neither one of them will show any data because of the final semi-colon (";").

Then create two formulas to display the data where you need it. They'll look like this:

{@ShowFirstAmount}
WhilePrintingRecords;
NumberVar firstAmount

{@ShowLastAmount}
WhilePrintingRecords;
NumberVar lastAmount

Note that there is no final semi-colon, so these will display the variable values. Place these in the section where you need to display the data.

-Dell