To solve this, I would just find what two adult tickets and one child ticket wold be worth.
To find that, just do:
5.20 + 9.90 * 2, which makes 25.
So now you just find how many 25s are in 900, or 36.
So 36 children's tickets were sold that day.
Hope I helped :)
The tree was approximately 40.8ft tall.
You use the equation, a^2+b^2=c^2.
12^2 + 39^2 = x^2, add the results of 12^2 and 39^2 to make 1665 = x^2. You can take the positive root of both sides, 3√185, and it equals 40.80441152, which is rounded to 40.8.
I think it represents the height hope that helps:)