Interpret Nuclear Equations Practice Test

In beta decay, a nucleus emits an electron ($^{0}{-1}\text{e}$). If $$^{A}{Z}\text{X} \rightarrow ^{A}{Z+1}\text{Y} + ^{0}{-1}\text{e},$$ what happens to the mass number $A$?

A nucleus undergoes beta (beta-minus) decay: $$^{131}{53}\mathrm{I} \rightarrow ,^{131}{54}\mathrm{Xe} + ,^{0}_{-1}\mathrm{e}.$$ What changes in the nucleus during this decay?