Question 28932
let the normal speed be 
If increased by 20 the speed will be x+20
Subtract the increase speed by the normal speed respect to the distance = time.


Equation:
{{{150/x-150/(x+20)=2}}}
{{{150((x)-(x+20))=2((x)(x+20))}}}
{{{150(20)=2(x^2+20x)}}}
{{{3000=2x^2+40x}}}
{{{2x^2+40x-3000}}}
{{{x^2+20x-1500=0}}}
a=1, b=20, c=-1500


{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}} 
{{{x=(-20+-sqrt(20^2-4*1*-1500))/(2*1)}}}
Simplfy that and you get 2 solutions:


x=-50 and x=30


Remove the negative


Hence, the normal speed (R) is 30mph.
Paul.