1. Identify the elements present:

* Calcium (Ca)

* Chlorine (Cl)

* Hydrogen (H)

* Carbon (C)

* Oxygen (O)

2. Count the atoms of each element on both sides:

| Element | Reactants | Products |

|---|---|---|

| Ca | 1 | 1 |

| Cl | 2 | 1 |

| H | 2 | 1 |

| C | 1 | 1 |

| O | 3 | 3 |

3. Adjust coefficients to balance the equation:

* Chlorine (Cl): We need 2 Cl atoms on the product side. Add a coefficient of 2 in front of HCl.

* Hydrogen (H): This is now automatically balanced with 2 H atoms on both sides.

4. The balanced equation is:

CaCl2 + H2CO3 → CaCO3 + 2HCl

Therefore, the coefficient needed to balance the equation is 2 in front of HCl.