How do I balance this nuclear decay equation?

Sum of atomic numbers on LHS = Sum of atomic numbers on RHS
20 = 19 + (Unknown atomic number)
Unknown atomic number = 1
The species having atomic number 1 and mass number 0 is a positron, with symbol β⁺ or e⁺.

The balanced nuclear equation is shown below:

Ricki is wrong.

The atomic numbers must add up to the same value, which is 20. On the right, the missing particle will be a +1.

The mass numbers must also add up to the same value, which is 41. Since they do, the mass number of the missing particle is zero.

The missing particle is a positron, not a proton. A proton has a +1 for the atomic number, but it also has a 1 for the mass number.

The equation is an example of a positron decay equation.