Question 907574
Let {{{ d }}} = the distance the 
slower car travels in 7 hrs
{{{ 665 - d }}} = the distance the 
faster car travels in 7 hrs
Let {{{ s }}} = the speed of the slower car
{{{ s + 45 }}} = the speed of the faster car
-------------------------------------
Equation for slower car:
(1) {{{ d = s*7 }}}
Equation for faster car:
(2) {{{ 665 - d = ( s + 45 )*7 }}}
----------------------------
Add the equations
(1) {{{ d = s*7 }}}
(2) {{{ 665 - d = ( s + 45 )*7 }}}
----------------------------
{{{ 665 = 7s + 7s + 315 }}}
{{{ 14s = 350 }}}
{{{ s = 25 }}}
and
{{{ s + 45 = 70 }}}
-----------------
The slower cars speed is 25 mi/hr
The faster car's speed is  70 mi/hr
------------------------------
check:
(1) {{{ d = s*7 }}}
(1) {{{ d = 25*7 }}}
(1) {{{ d = 175 }}}
and
(2) {{{ 665 - d = ( s + 45 )*7 }}}
(2) {{{ 665 - d = 70*7 }}}
(2) {{{ d = 665 - 490 }}}
(2) {{{ d = 175 }}}
OK