Question 647835
Almost there
{{{ x }}} = price of adult tickets 
{{{ y }}} = price of child tickets 
(1) {{{ 4x + 8y = 140 }}}
(2) {{{ 4x + 2y = 80 }}}
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Subtract (2) from (1)
(1) {{{ 4x + 8y = 140 }}}
(2) {{{ -4x - 2y = -80 }}}
{{{ 6y = 60 }}}
{{{ y = 10 }}}
Now plug this result back into
either (1) or (2)
(2) {{{ 4x + 2*10 = 80 }}}
(2) {{{ 4x = 80 - 20 }}}
(2) {{{ 4x = 60 }}}
(2) {{{ x = 15 }}}
$15 = price of an adult ticket 
$10 = price of a child ticket
check:
(1) {{{ 4*15 + 8*10 = 140 }}}
(1) {{{ 60 + 80 = 140 }}}
(1) {{{ 140 = 140 }}}
OK