Concept:The given equations do not follow standard addition. Instead, the two numbers are simply placed side by side (concatenated) to form a new number.Explanation:In 8+1=81, the digits 8 and 1 are written together as 81 (not added to get 9).Similarly, 6+3=63 means we write 6 then 3 to get 63.Following the same pattern, 5+4 means write 5 then 4, giving 54.So the answer is 54, which matches option C.Answer:Option C: 54