Question 66138
The number is {{{10a + b}}} The digits are a and b
{{{a + b = 7}}}
{{{a = 2b + 7}}}
{{{b = 7 - a}}}
{{{a = 2(7 - a) + 7}}}
{{{a = 14 - 2a + 7}}}
{{{a = 21 - 2a}}}
{{{3a = 21}}}
{{{a = 7}}}
{{{7 + b = 7}}}
{{{b = 0}}}
The number is 70
If b were 1 or greater, a would turn out to be 9 or higher, and
a can't be greater than 7
{{{a = 2*1 + 7}}}
{{{a = 9}}}