Question 149182
Let {{{t}}} = the tens digit
Let {{{u}}} = the units digit
(1){{{t + u = 3}}}
(2){{{t = u + 1}}}
substitute the expression for {{{t}}} in (2) for {{{t}}} in (1)
{{{u + 1 + u = 3}}}
{{{2u = 2}}}
{{{u = 1}}}
and since
{{{t + u = 3}}}
{{{t + 1 = 3}}}
{{{t = 2}}}
The number is 21
This checks with (1) and (2)