The superscripts are the atomic mass numbers(A). The sum of them is the A for the left-hand-side particle or 243.
The subscripts are the atomic number (or + charge, Z) Note that the β particle, a high-energy electron released from the nucleus as a result of β-decay, has "no mass compared to a proton" and a -1 charge. Again the sum of the Z's must be the atomic number of the particle on the left. (94)
You look up the element with that atomic number.
