unable to install ubuntu

hi guys. i installed ubuntu on my macbook after partitioning the hard disk. i allocated 20gb for it using disk utility. Since i have not found much use of ubuntu i need to remove it. i am stumped as i have no idea as to what has to be done. i open disk utility to delete the partition but i get this message as u can see frm the pic. plz help me guys.

You can't use Boot Camp Assistant to restore it unless you used Boot Camp Assistant to create the partition.

Since you used Disk Utility to create the partition, you'll have to use Disk Utility to restore it to a single partition.

Follow directions here - but you may need to boot from the OS X disc and open up Disk Utility from there - and make sure you have a backup before you begin.