Question 935180
Let {{{ d }}} = the distance in miles
between their houses
Let {{{ t }}} = the time in hours for
Ahmad to go from his house 
to his friend's house
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Equation for Ahmad's house to friend's house:
(1) {{{ d = 60t }}}
Equation for friend's house to Ahmad's house:
(2) {{{ d = 50*( 11 - t ) }}}
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By substitution:
(2) {{{ 60t = 50*( 11 - t ) }}}
(2) {{{ 60t = 550 - 50t }}}
(2) {{{ 110t = 550 }}}
(2) {{{ t = 5 }}}
and
(1) {{{ d = 60t }}}
(1) {{{ d = 60*5 }}}
(1) {{{ d = 300 }}}
It is 300 miles to Ahmad's friend's house
check:
(2) {{{ d = 50*( 11 - t ) }}}
(2) {{{ 300 = 50*( 11 - 5 ) }}}
(2) {{{ 300 = 50*6 }}}
(2) {{{ 300 = 300 }}}
OK