it seems to be a 2 digit numbber since we are only told up to the tens digit
xy is te number
x=tens digit
y=ones digit
x is one less than 3 times y
x=-1+3y
y has to be a whole/counting number
if y=1
x=-1+3(1)
x=-1+3
x=2
number could be 21
if y=2
x=-1+3(2)
x=-1+6
x=5
number could be 52
if y=3
x=-1+3(3)
x=-1+9
x=8
number could be 83
number could be 21, 52, 83
sum of digits is 11
2+1=3, nope
5+2=7 nope
8+3=11 correct
number is 83
(it could easily be 821 or 452, )
numer is 83