Question 731514
Let {{{ s }}} = Luis's speed in mi/hr
{{{ 4s }}} = Pedro's speed in mi/hr
Let {{{ t }}} = Pedro's time in hrs to travel 36 mi
{{{ t + 3 }}}  = Luis's time in hrs to travel 36 mi
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Pedro's equation:
(1) {{{ 36 = (4s)*t }}}
Luis's equation:
(2) {{{ 36 = s*( t + 3 ) }}}
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(1) {{{ t = 9/s }}}
(2) {{{ 36 = s*( 9/s + 3 ) }}}
(2) {{{ 36 = 9 + 3s }}}
(2) {{{ 3s = 27 }}}
(2) {{{ s = 9 }}}
Luis's speed is 9 mi/hr
check:
(1) {{{ t = 9/s }}}
(1) {{{ t = 9/9 }}}
(1) {{{ t = 1 }}} hr
and
(2) {{{ 36 = 9*( t + 3 ) }}}
(2) {{{ 36 = 9t + 27 }}}
(2) {{{ 9t = 9 }}}
(2) {{{ t = 1 }}} hr
OK