Question 662380
Let {{{ s }}} = the speed of the lift in km/hr
{{{ 5s }}} = speed skiing in km/hr
Let {{{ t }}} = time to go up mountain on lift in hrs
{{{ 3/4 - t }}} = time spent skiing in hrs 
---------
Equation for lift:
(1) {{{ 7/4 = s*t }}}
Equation for skiing:
(2) {{{ 7/4 = 5s*( 3/4 - t ) }}}
------------------------
(1) {{{ t = (7/4)*(1/s) }}}
Substitute this into (2)
(2) {{{ 7/4 = 5s*( 3/4 - (7/4)*(1/s) ) }}}
(2) {{{ 7/4 = (1/4)*( 15s - 7/s) }}}
(2) {{{ 7 = 15s - 7/s }}}
(2) {{{ 7s = 15s^2 - 7 }}}
(2) {{{ 15s^2 - 7s - 7 = 0 }}}
Use the quadratic equation to solve for {{{s}}} in km/hr
Have to run- good luck