Question 738955
Let {{{ t }}} = her time in hrs for the 1st trip
{{{ 7-t }}} = her time for the trip back
Let {{{ d }}} = distance to grandmother's house
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(1) {{{ d = 60t }}}
(2) {{{ d = 45*( 7 - t ) }}}
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Substitute (1) into (2)
(2) {{{ 60t = 45*( 7 - t ) }}}
(2) {{{ 60t = 315 - 45t }}}
(2) {{{ 105t = 315 }}}
(2) {{{ t = 3  }}}
and
(1) {{{ d = 60t }}}
(1) {{{ d = 60*3 }}}
(1) {{{ d = 180 }}}
The distance to grandmother's house is 180 mi
check:
(2) {{{ d = 45*( 7 - t ) }}}
(2) {{{ 180 = 45*( 7 - 3 ) }}}
(2) {{{ 180 = 45*4 }}}
(2) {{{ 180 = 180 }}}
OK