a brother and sister left their house at the same time The b

a brother and sister left their house at the same time. The brother headed east on his bike riding 13 miles per hour. The sister headed west on her skateboard riding 5 miles per hour. How long will it take them to be 9 miles apart?

Solution

13*t+5*t=9
(13+5)*t=9
18t=9
t=1/2hour
check
5*.5+13*.5=
2.5+6.5=9 miles