chemical equation
(a) NaOH +HCL --->NaCl +H2O
(b) THE number of moles reacted is = molarity x volume in litres
hence the number of moles of NaOH=(o.201 x 30.5ml)/100ml=0.00613 moles
(C) the number of moles of Hcl that were reacted, from the reaction above the recting ratio of NaOH to HCl is 1:1 thus the moles of HCl is also 0.00613
(D) my of HCl is =moles/volume in litres
that is (0.00613/20) x 1000=0.306M