X - y = 2400/6 = 400 where x = speed of plane and y = speed of wind.
x + y = 2400/5 = 480 - flying with the wind
adding the 2 equations
2x = 880
x = 440
Speed of the plane with no wind = 440 mph
Don’t Identify- 278.98
Female- 450.66
Male- 343.36
Considering these are people, you probably will need to round either up or down. If you round it would be:
Don’t Identify- 279
Female- 451
Male- 343
Steps 4 and 5 are being used to get the equation in step 6.
Steps 5 and 7 are being used to get the equation in step 8.
Steps 8 and 6 are being used to get the equation in step 9.
In step 14, "similar argument" means to draw segment BD and follow the same logic in steps 3-12.
You can only add exponents if you are multiplying two of the same variable together. For example,

You take them away if you are dividing.
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In a polynomial equation, you can add together two of the same variable if they have the same exponent
</span>

Or you can take them away in a similar fashion,
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But you cannot add two (or more) different exponents,
</span>

(it does not get any simpler)
I hope this has answered your question, if not, leave a comment and I'll update the answer.