Answer:
a. 
b. 
Explanation:
Using the triangle theorem both triangle the woman makes between the light so the rate of change of length can use geometry first

Solve to find the rate relation


Now the rate of the change rate


Finally the rate of her shadow moving


Down stream it would be going 20 mph and up stream 10 mph
To calculate force, use the formula force equals mass times acceleration, or F = m × a. Make sure that the mass measurement you're using is in kilograms and the acceleration is in meters over seconds squared. When you've solved the equation, the force will be measured in Newtons.
15.0 I’m pretty sure that’s the answer to your question