Question 162773
D=RT OR D/R=T
SEEING AS THE TIMES ARE THE SAME. 
THEN:
600/(R+10)=500/R
500(R+10)=600R
500R+5,000=600R
500R-600R=-5,000
-100R=-5,000
R=-5,000/-100
R=50 MPH FOR SUSAN.
50+10=60 MPH FOR BEVERLY.
PROOF:
600/60=500/50
10=10