Balance the Following Equation for an Oxidation-Reduction Reaction Occurring in an Acidic

Balance the following equation for an oxidation-reduction reaction occurring in an acidic solution:
HCl(aq) + H₂C₂O₄(aq) + MnO₂(s) → MnCl₂(aq) + CO₂(g) + H₂O(l)
The sum of the coefficients is ________.

A) 7
B) 15
C) 45
D) 12
E) 9