Question 577216
Let {{{ a }}} = 10's digit
Let {{{ b }}} = unit's digit
given:
(1) {{{ a + b = 8 }}}
(2) {{{ 10b + a  = 10a + b - 18 }}}
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(2) {{{ 10a - a - 10b + b = 18 }}}
(2) {{{ 9a - 9b = 18 }}}
(2) {{{ a - b = 2 }}}
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Add equations (1) and (2) 
{{{ 2a = 10 }}}
{{{ a = 5 }}}
and, since
(1) {{{ a + b = 8 }}}
(1) {{{ 5 + b = 8 }}}
(1) {{{ b = 3 }}}
The original number is 53
check:
(2) {{{ 10b + a  = 10a + b - 18 }}}
(2) {{{ 10*3 + 5  = 10*5 + 3 - 18 }}}
(2) {{{ 35 = 53 - 18 }}}
(2) {{{ 35 = 35 }}}
OK