Question 635016
Let {{{ t }}} = time spent traveling by boat
{{{ 42 - t }}} = time spent traveling by plane
Let {{{ r }}} = rate by boat
Let {{{ 20r }}} = rate by plane
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Equation for boat:
(1) {{{ 640 = r*t }}}
(2) {{{ 640 = 20r*( 42 - t ) }}}
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(2) {{{ 640 = 840r - r*t }}}
Substitute (1) into (2)
(2) {{{ 640 = 840r - 640 }}}
(2) {{{ 1280 = 840r }}}
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You can finish. Find {{{ r }}}
and {{{ 20r }}}