Disk 1.
You can't merge those 2 large partitions due to the 450MB partition in the middle.
Solution.
Delete that 450MB partition.
That will make that whole left part one big unallocated space.
You should then be able to merge that with the partition on the right.
Of course, you should have a full backup of any data you wish to keep.
It's easy to screw up the whole drive doing this.