Answer is: mass number stays 184, but atomic number changes.
Beta decay is radioactive decay in which a beta ray and a neutrino are emitted from an atomic nucleus.
There are two types of beta decay: beta minus and beta plus. In beta minus decay (atomic number Z is increased by one, new element is wolfram W) neutron is converted to a proton and an electron and an electron antineutrino.
In beta plus decay (atomic number Z is decreased by one, new element is hafnium Hf), a proton is converted to a neutron and positron and an electron neutrino, so mass number does not change.