Let x = Ted' speed, in miles per hour.
Then the Alivia' speed is (x+4) mph.
Write the time equation
= hours.
Solve it. Start cross-multiplying; then simplify
30x = 15*(x+4)
30x = 15x + 60
30x - 15x = 60
15x = 60
x = 60/15 = 4.
ANSWER. Ted' speed is 4 mph. Olivia' speed is 4+4 = 8 mph.