A jogger runs in a straight line with an average velocity of 5m/s for 4 min, and then with an average velocity of 4m/s for 3 min. (a) what is her total displacement? (b) what is her average velocity during this time?

Velocity = \frac{Displacement}{Time}

Use that formula, then add the two values for displacement you get.

Average Speed = \frac{Total Displacement}{Total Time}

And be sure that you are using the correct units. Velocity is seconds, convert every time into seconds.