For this case, the first thing we must do is define variables:
p: plane speed
w: wind speed
With the wind in favor, the speed is:

With the wind against the speed is:

Rewriting both equations, we have the following system of equations:

Then, solving the system of equations (graphically for example), we have the solution is:

Therefore, jet stream's speed:
Answer:
A) p + w = 960; p - w = 600; jet stream's speed = 180 km / h
4 and 15. You can guess and check or use algebra.
The angles diagonally opposite each other are congruent while those adjacent to each other add up to 180 degrees. You can get eight congruent angles with a transversal if the two lines are parallel, because each angle would be 90.