During transcription, an mRNA molecule is synthesized complementary to one of the DNA strands, known as the template strand. Using the DNA sequence you provided (AGC GCT), the mRNA strand would be:

mRNA sequence: UGC CGA

Remember that thymine (T) in DNA is replaced by uracil (U) in RNA. The mRNA sequence is the reverse complement of the non-template (coding) strand of DNA.