creating table from multiple other columns

Hit the New Table button and add this DAX formula:

new table = ADDCOLUMNS(
	NATURALINNERJOIN(
		'Table 1',
		SUMMARIZE(
			'Table 2',
			'Table 2'[closing balance]
		)
	),
	"sum balance",
	'Table 1'[opening balance] + 'Table 2'[closing balance]
)

Note that you need to have a relationship between the two source tables. Also if your real data is not quite like this sample data, you may have to use NATURALLEFTOUTERJOIN instead. Depends on whether or not one of the two tables has blanks or duplicates.