Respuesta :
list digits and add
3+1=4
3+2=5
3+3=6
3+4=7
....
we seee the only number less than 5 is 4
31 is da number
3+1=4
3+2=5
3+3=6
3+4=7
....
we seee the only number less than 5 is 4
31 is da number