.
= 990 = x + y (1) is the effective speed with the wind.
= 900 = x - y (2) is the effective speed against the wind.
Add the equations (1) and (2) to get
2x = 990 + 900 = 1890 ====> x = 1890/2 = 945.
Then y = 990 - x = 990 - 945 = 45.
Answer. The plane speed is 945 kilometers per hour and the wind speed is 45 kilometers per hour.
It is a typical "tailwind and headwind" word problem.
See the lessons
- Wind and Current problems
- Wind and Current problems solvable by quadratic equations
- Selected problems from the archive on a plane flying with and against the wind
in this site, where you will find other similar solved problems with detailed explanations.
Also, you have this free of charge online textbook in ALGEBRA-I in this site
ALGEBRA-I - YOUR ONLINE TEXTBOOK.
The referred lessons are the part of this textbook under the section "Word problems", the topic "Travel and Distance problems".
Save the link to this online textbook together with its description
Free of charge online textbook in ALGEBRA-I
https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson
to your archive and use it when it is needed.