DV = Const. + β1* IV+ ε (if β1 is significant)

Med. V = Const. + β2* IV+ ε (if β2 is significant)

DV = Const. + β1* IV+ β3* Med. V+ ε (β1 should be insignificant)

I think for the question you have asked it is (me+X1) but β is what we are worried about. So it will be (β1* Me + β2*X1)

Hope this clarifies your doubt

Dear Ramesh Kumar, I can understand what you mean, but could you provide me article or any Ref related to that.

thank you very much