You can add computed column with AS keyword followed by your computed formula.
Note: the computed column cannot be updated!
CREATE TABLE #tmp
(
[hours] float,
[rate] float
)
ALTER TABLE #tmp ADD salary AS ([hours] * [rate])
INSERT INTO #tmp([hours], [rate])
SELECT 160, 10
UNION
SELECT 180, 12
SELECT * FROM #tmp
--The column "salary" cannot be modified because it is either a computed column or is the result of a UNION operator.
--update #tmp
--set salary = salary *1.14
drop table #tmp
