Question 458690
David speed = 30 mph
Anna speed = x mph

Anna leaves after 1 hour

In 1 hour David has traveled 30 miles
So catch up distance = 30 miles.
Anna is 10 miles ahead of David after 4 hours
30+10 = 40 miles

catch up time = 4 hours
catch up speed = x-30

r=d/t
x-30=40/4
4(x-30)= 40
4x-120=40
4x=120+40
4x=160
x=40 mph speed of Anna