Question 726059
Let {{{ a }}} = Louis's age now
Let {{{ b }}} = Mackenzie's age now
{{{ a + 8 }}} = Louis's age in 8 years
{{{ b + 8 }}}= Mackenzie's age in 8 years
given:
(1) {{{ a = 3b }}}
(2) {{{ a + 8 + b + 8 = 100 }}}
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(2) {{{ a + b + 16 = 100 }}}
(2) {{{ a + b = 84 }}}
Substitute (1) into (2)
(2) {{{ 3b + b = 84 }}}
(2) {{{ 4b = 84 }}}
(2) {{{ b = 21 }}}
and, since
(1) {{{ a = 3b }}}
(1) {{{ a = 3*21 }}}
(1) {{{ a = 63 }}}
Louis is 63 and Mackenzie is 21 
check:
(2) {{{ a + b + 16 = 100 }}}
(2) {{{ 63 + 21 + 16 = 100 }}}
(2) {{{ 100 = 100 }}}
OK