Actually in question they said that we have only half adders so as to implement a full adder we need two half adder and one OR gate ,that OR gate should also be implemented using half adder only and to implement one OR gate we need two half adder so overall to implement one full adder we need only 4 half adders.
Now, to implement (m-1) full adder we need 4*(m-1) half adders.
Therefore,to add two m bit numbers we need total 4*(m-1)+1=4m-3 half adders.
Thus all options are incorrect.