Hi, I am having trouble getting started on this physics problem...it seems fairly simple just need some hints:

You drive on Interstate 10 from San Antonio to Houston, half thetimeat 73 km/h and the other half at 90 km/h. On the way back you travel half thedistanceat 73 km/h and the other half at 90 km/h. What is your average speeda)from San Antonio to Houston,b)from Houston back to San Antonio, and(c)for the entire trip?I know average speed is the total distance during the trip divided by the total time for the trip but I am not sure how to determine those.

Thanks.