How Fast Must the Race Car Go in the Last 2 Laps to Qualify?

[katyross]

Homework Statement

"A race car driver must average 180 km/h for 4 laps to qualify for a race. Because of engine trouble, the car averages only 150 km/h over the first 2 laps. What speed must be maintained for the last 2 laps?"

Homework Equations

v= d/t

The Attempt at a Solution

i actually have no idea where to start with this

 

[rl.bhat]

Find total time for 4 laps with average velocity 180 km/h.
Find total time for 2 laps with average velocity 150 km/h.
Find total time for remaining 2 laps with average velocity v km/h.
Equate the first one with the sum of the other two.