since the model number has 42, i would say it probably is a 3 1/2 ton.
The Rheem model RBHJ 21J11SUBA1 is a 2-ton air conditioning unit.
2 ton
model 030 = 30,000 BTU = 2.5 TON
2 ton.
That isn't a typical Rheem model number, are you sure that isn't the serial? If it is the model number it is a 2.5 ton :)
3-ton
3 TON
4 ton
3 ton
2 ton
5 ton
two ton