Question 1004968
Jane's head start in miles:
{{{ 4*(1/4) = 1 }}} mi
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Now imagoine that you start a stopwatch 
when Bill leaves.
Let {{{ t }}} = time in hours on stopwatch
when Bill catches Jane
Let {{{ d }}} = distance in miles Bill travels
until he catches up with Jane
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Bills equation:
(1) {{{ d = 8t }}}
Jane's equation:
(2) {{{ d - 1 = 4t }}}
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Substitute (1) into (2)
(2) {{{ 8t - 1 = 4t }}}
(2) {{{ 4t = 1 }}}
(2) {{{ t = 1/4 }}}
It will take Bill 15 min to catch Jane
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check:
(1) {{{ d = 8t }}}
(1) {{{ d = 8*(1/4) }}}
(1) {{{ d = 2 }}}
and
(2) {{{ d - 1 = 4t }}}
(2) {{{ d - 1 = 4*( 1/4) }}}
(2) {{{ d - 1 = 1 }}}
(2) {{{ d = 2 }}}
OK