Question 893133
Let {{{ d }}} = the distance in miles he drives on highway 
Let {{{ t }}} = time in hours he spends on highway 
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Now convert {{{ 5 }}} minutes to hours
( minutes ) x ( hours / minute )
{{{ 5*( 1/60 )  = 1/12 }}} hrs
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Equation for driving on highway:
(1) {{{ d = 45t }}}
Equation for driving on local roads:
(2) {{{ d - 3 = 36*( t + 1/12 ) }}}
(2) {{{ d = 36t + 3 + 3 }}}
(2) {{{ d = 36t + 6 }}}
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Substitute (1) into (2)
(2) {{{ 45t = 36t + 6 }}}
(2) {{{ 9t = 6 }}}
(2) {{{ t = 2/3 }}} hrs
and, since
(1) {{{ d = 45t }}}
(1) {{{ d = 45*(2/3) }}}
(1) {{{ d = 30 }}}
He drove 30 highway miles
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check:
(2) {{{ d - 3 = 36*( t + 1/12 ) }}}
(2) {{{ 30 - 3 = 36*( 2/3 + 1/12 ) }}}
(2) {{{ 27 = 36*( 8/12 + 1/12 ) }}}
(2) {{{ 27 = 36*( 9/12 ) }}}
(2) {{{ 27 = 3*9 }}}
(2) {{{ 27 = 27 }}}
OK