At The End
Excel will automatically expand formulas at the end of a formula range if they refer to three or more consecutive rows or columns.
Inserting a row underneath March and entering a number into cell "C6" will cause the SUM() formula in cell "C7" to automatically expand.
The SUM() formula will only expand automatically if you enter numerical data into cell "C6".
Formulas will not be expanded automatically if you insert rows (or columns) at the start of a formula range.