We have:
631 ÷ (251+321) of 331
= 319 ÷ (511+27) of 310 [Converting mixed to improper fraction]
According to BODMAS rule, we simplify brackets first
=319÷(1022+35) of 310=319÷1057 of 310=319÷1057×310=319÷30570=319÷119=319×191=31[Bracket simplified][Of simplified][Reciprocal of 119 is 191][Division simplified]
∴ The answer is 31