a) `12.53+53.172-84.53`
`= 53.(12+172-84)`
`= 53.100`
`= 5300`
b) `35.34+35.86+65.75+45.65`
`= 35.(34+86)+65.(75+45)`
`= 35.120+65.120`
`= 120.(35+65)`
`= 120.100`
`= 12000`
c) `3.25.8+4.37.6+2.12.38`
`= 24.25+24.37+24.38`
`= 24.(25+37+38)`
`= 24.100`
`= 2400`