David drove for 3 hours at a rate of 50 miles per hour.for 2 hours at 60 miles per hour and for 4 hours at a rate of 70 miles er hour.what was his constant-speed for the whole journey?

David drove for 3 hours at a rate of 50 miles per hourfor 2 hours at 60 miles per hour and for 4 hours at a rate of 70 miles er hourwhat was his constantspeed f class=