Question 319987
let her speed be x
increased speed = x+10
distance traveled=120 miles
36/60 = 3/5 hours
..
time taken with increased speed= original time -3/5 hours
120/x+10= 120/x  -3/5
120/x+10=600-3x /5x
5x*120=(x+10)(600-3x)
600x=600x-30x+6000-3x^2
3x^2+30x-6000=0
x^2+10x-2000=0
x^2+50x-40x-2000=0
x(x+50)-40(x+50)=0
(x+50)(x-40)=0
x=40 mph