Answer: The allowable ampacity is 136 amperes
Explanation:According to the National Electrical Code the ampacity for insulated conductors of type 1/0 AWG THHN is 170 amperes(from tables) for cables no exceeding 3
But we are presented with 4 cables in a tray,
Going by the National Electrical Code where conductors exceeds 3, the allowable ampacity shall be reduced to 80% the of the ampacity gotten from table.
Hence the allowable ampacity for 4 copper cables of type 1/0 AWG THHN is (80/100) *170=136 Amperes