Your question is Tennis Balls in an Airplane. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
How many tennis balls fit in an aeroplane?
Estimate the answer using explicit assumptions about aircraft size, usable interior volume, and packing efficiency. State your assumptions clearly, show the math, and explain any major simplifications. Focus on a defensible estimate, not a precise real-world count.