A is a solution containing 3.5g of an acid Hx per dm3
B is a solution containing  0.50mole of anhydrous Na2CO3 per dm3 of solution.  25cm3 portions of solution B required an average volume of 26.10cm3 of solution A for complete neutralization.  From these results,  calculate
a.  Molar concentration of solution A
b. The relative molecular mass of A