Question 536716
speed of car = x 
speed of train = x+20

d=240
t=d/r

time car - time train = 1/2 hour

(240/x)-240/(x+20)=1/2

LCD = x(x+20)

240(x+20)-240x= x(x+20)/2
240x+4800-240x=(x^2+20x)/2
9600=x^2+20x

x^2+20x-9600=0

Find the roots of the equation by quadratic formula						
						
a=	1	,b=	20	,c=	-9600	
						
b^2-4ac=	400	+	38400			
b^2-4ac=	38800					
{{{x=(-b+-sqrt(b^2-4ac))/(2a)}}}						
{{{x1=(-b+sqrt(b^2-4ac))/(2a)}}}						
{{{x1=(-12+21)/(12)}}}						
x1=(	-20	+	196.98	)/	2	
x1=	88.49	88 43/88				
x2=(	-20	-196.98	) /	2		
x2= 	-108.49					
Ignore negative value						
car speed	=	88.49	mph