NUMERAL : UEALRMN : : ALGEBRA : ?

Expression = NUMERAL : UEALRMN

The letters at odd position (starting from left) are written in reverse order at the end of the code, while the letters at even position are written as it is at the start of the code.

Letters at even position = UEA -> UEA (placed at the beginning)

Letters at odd position of the NUMERAL = NMRL -> LRMN (placed at the end)

Similarly, for ALGEBRA :

Letters at even position = LER -> LER

Odd position = AGBA -> ABGA

Thus, ALGEBRA : LERABGA

=> Ans - (D)