RH₂  (ion exchange resin) can replace ${\mathrm{Ca}}^{2+}$ ions in hard water as ${\mathrm{RH}}_2+{\mathrm{Ca}}^{2+}\to \mathrm{RCa}+2{\mathrm{H}}^{+}.$
If 1 L of hard water after passing through ${\mathrm{RH}}_2\mathrm{has}\mathrm{pH}=3$ then hardness in parts per million of Ca²⁺ is equal to