Sally walks to the store at a rate of 3 m/s for 15 seconds. She stops at a crosswalk for 4 seconds until the sign tells her she can go. Sally ran across the street at 5 m/s for 3 seconds until she reached the other side. She then walked the rest of the way to the store at 3 m/s. If the store was 100 m away from where Sally started originally and it took her 250 seconds to get there, what was her average speed?