Question 617107
Let {{{ j }}} = Javier's speed
Let {{{ k }}} = Keiko's speed
given:
(1) {{{ k = j + 8 }}}
(2) {{{ 30/j = 54/k }}}
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Substitute (1) into (2)
(2) {{{ 30/j = 54/( j + 8 ) }}}
(2) {{{ 30*( j + 8 ) = 54j }}}
(2) {{{ 30j + 240 = 54j }}}
(2) {{{ 24j = 240 }}}
(2) {{{ j = 10 }}}
and, since
(1) {{{ k = j + 8 }}}
(1) {{{ k = 10 + 8 }}}
(1) {{{ k = 18 }}}
Javier travels 10 km/h 
Keiko travels 18 km/h
check:
(2) {{{ 30/10 = 54/18 }}}
(2) {{{ 3 = 3 }}}
OK