Question 697297
I think you have to draw a number line and
then show just where the 2 numbers are
that you are looking for.  Here's the line and
numbers you are interested in

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 ^ n[1] . . . . .^ 11. . . . . . . . . . . . .^ 19

In this situation, I have
(1) {{{ 3* ( 11 - n[1] ) = 19 - n[1] }}}

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The other situation looks like:

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   ^ 11 . . . . ^ n[2] . . . . . . . . . . . ^ 19

I can write this as:
(2) {{{  3*( n[2] - 11 )  = 19 - n[2] }}}
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(1) {{{ 33 - 3n[1] = 19 - n[1] }}}
(1) {{{ 2n[1] = 33 - 19 }}}
(1) {{{ 2n[1] = 14 }}}
(1) {{{ n[1] = 7 }}}
and
(2) {{{  3*( n[2] - 11 )  = 19 - n[2] }}}
(2) {{{ 3n[2] - 33 = 19 - n[2] }}}
(2) {{{ 4n[2] = 52 }}}
(2) {{{ n[2] = 13 }}}
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The numbers are 7 and 13, and the sum is:
{{{ 7 + 13 = 20 }}} answer
check answer:
(1) {{{ 3* ( 11 - n[1] ) = 19 - n[1] }}}
(1) {{{ 3* ( 11 - 7 ) = 19 - 7 }}}
(1) {{{ 3*4 = 12 }}}
(1) {{{ 12 = 12 }}}
and
(2) {{{  3*( n[2] - 11 )  = 19 - n[2] }}}
(2) {{{  3*( 13 - 11 )  = 19 - 13 }}}
(2) {{{ 3*2 = 6 }}}
(2) {{{ 6 = 6 }}}
OK