Question 454779
There are 2 different rates, so you need 2 different equations:
Let {{{ r }}} = driving speed
Let {{{ t }}} = time spent driving
In car:
{{{ d = r*t }}}
(1) {{{ 45 = r*t }}}
Walking:
(2) {{{ 3 = (r/15)*(1.5 - t) }}} ( units in miles, hrs,  and miles/hr )
There are 2 equations and 2 unknowns, so it's solvable
(2) {{{ 3 = (r/15)*(1.5 - t) }}}
(2) {{{ 3 = r/10 - (1/15)*r*t }}}
Substitute (1) into (2)
(2) {{{ 3 = r/10 - 45/15 }}}
(2) {{{ 3 = r/10 - 3 }}}
(2) {{{ r/10 = 6 }}}
(2) {{{ r = 60 }}} mi/hr
check answer:
(1) {{{ 45 = r*t }}}
(1) {{{ t = 45/60 }}}
(1) {{{ t = .75 }}} hrs
and
(2) {{{ 3 = (60/15)*(1.5 - .75) }}}
(2) {{{ 3 = 4*.75 }}}
(2) {{{ 3 = 3 }}}
OK