The equation you can use to solve the problem is;
50/30 = 300/x
Next Cross Multiply
50x = 9000
x = 9000/50
x = 180
The building's shadow is 180 feet tall
If she went back 5 miles than the displacement would be 0.
Just subtract the amount of miles she went back from the miles she went forward 5 - 5 = 0
Be more specific I’m not understanding your question?
