Question 945846
Let {{{ n }}} = Nelson's age now
Let {{{ c }}} = Charlie's age now
{{{ c - 4 }}} = Charlie's age 4 years ago
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(1) {{{ n = 2*( c - 4 ) }}}
(2) {{{ n + c = 34 }}}
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(1) {{{ n = 2c - 8 }}}
(1) {{{ -n + 2c = 8 }}}
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Add (1) and (2) 
(2) {{{ n + c = 34 }}}
(1) {{{ -n + 2c = 8 }}}
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{{{ 3c = 42 }}}
{{{ c = 14 }}}
and
(1) {{{ n = 2c - 8 }}}
(1) {{{ n = 2*14 - 8 }}}
(1) {{{ n = 28 - 8 }}}
(1) {{{ n = 20 }}}
Nelson is 20
Charlie is 14
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check:
(2) {{{ n + c = 34 }}}
(2) {{{ 20 + 14 = 34 }}}
(2) {{{ 34 = 34 }}}
OK