<Tr> <Th> Ca </Th> <Td> 2.086% </Td> <Td_colspan="4"> stable </Td> </Tr> <Tr> <Th> Ca </Th> <Td> syn </Td> <Td> 162.7 d </Td> <Td> β </Td> <Td> Sc </Td> </Tr> <Tr> <Th> Ca </Th> <Td> 0.004% </Td> <Td_colspan="4"> stable </Td> </Tr> <Tr> <Th> Ca </Th> <Td> syn </Td> <Td> 4.5 d </Td> <Td> β </Td> <Td> Sc </Td> </Tr>

What’s the mass number of the isotope of calcium (ca) containing 20 neutrons