The rule of pairing of base-pair says that A and T base pairs with each other with two hydrogen bonds and G and C base pairs with each other with three hydrogen bonds in DNA. In the case of RNA Uracil comes at the place of thymine that means uracil replaces thymine.
Therefore according to this base-pairing rule the corresponding codon of mRNA transcribes from DNA codon 5' AGT 3' will be 3' UCA 5' as U came in place of A nucleotide, C comes in place of G nucleotide, and A comes in place of T nucleotide.
