Question 118717
note that "{{{v}}}" is the variable for speed, that "{{{d}}}" is the variable for distance, and that "{{{t}}}" is the variable for time
the {{{42km}}} drive from Oakdale to Ridgemont is your distance {{{d}}}

the time {{{t = 28 min}}}

the speed is: 

 {{{v = d/t}}}

Then usual speed is: 

{{{v = 42km/28min}}}….divide both sides by {{{14}}}


{{{v = 3km/2min}}}


{{{v = (3/2)(km/min)}}}…………..since {{{1min}}} is {{{(1/60)h}}}, we will have


{{{v = ((3/2)/(1/60))(km/h)}}}…………..


{{{v = (3*60)km/(2h)}}}…………..simplify


{{{v = (3*30)km/h}}}…………..


{{{v = 90(km/h)}}}


let a reduced speed limit be {{{v[1]}}}


distance remain same 


{{{v[1] = d/t[1]}}}


since the trip now takes {{{14 min}}}{{{ longer}}}, we can write the time as 


{{{t[1] = t + 14min}}} which is {{{t[1] = 28min + 14min}}}, or 

{{{t[1]= 42min}}}

then


{{{v[1] = 42*km/42*min}}}
	

{{{v[1] = (42/42)(km/min)}}}


{{{v[1] = 1(km/min)}}}………. {{{1min}}} is {{{ (1/60)*h }}}, then we will have


{{{v[1] = 1km/(1/60)h}}}……….


{{{v[1] = 60*(km/h)}}}………. a reduced speed limit