Need help with subtotals

[DRStein]

RO Number	Cost	Subtotal
12345	50	0
12345	75	0
12345	25	150
67890	100	0
67890	50	0
67890	50	0
67890	200	400

<tbody>
</tbody>

I would like to know if there is a formula to total by RO Number. I have multiple RO numbers some only contain one line with one unique RO Number and as you can see there are multiple costs for the same RO Number. Is there a way to calculate the subtotal in an Excel table?
Thanks!

 

[steve the fish]

This would do it:

=SUMIF($A$1:$A$100,$A$1:$A$100,$C$1:$C$100)

 

[DRStein]

Thanks that worked!