Question 945673
Let {{{ k }}} = Karen's age
Let {{{ j }}} = Joe's age
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(1) {{{ k = 4j  + 13 }}}
(2) {{{ k + j = 73 }}}
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Substitute (1) into (2)
(2) {{{ 4j + 13 + j = 73 }}}
(2) {{{ 5j + 13 = 73 }}}
(2) {{{ 5j = 60 }}}
(2) {{{ j = 12 }}}
and
(2) {{{ k + j = 73 }}}
(2) {{{ k = 73 - j }}}
(2) {{{ k = 61 }}}
Karen is 61
Joe is 12 
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check:
(1) {{{ k = 4j  + 13 }}}
(1) {{{ 61 = 4*12 + 13 }}}
(1) {{{ 61 = 48 + 13 }}}
(1) {{{ 61 = 61 }}}
OK