Answer this quadratic word problems? please!

Q1: Find two consecutive odd integers such that their sum is 40 and their product is 399.

note: i know the answer(19, 21(this is a wild guess)) but i don't how to do it using quadratic equation. please give the formula or the equation only.

Q2: Gardening. A square garden has an area of 1764 squared feet, and the gardener wants to install a sprinkler (with a circluar spraying pattern) at the center of the garden. What is the minimum radius of spray the sprinkler would need in order to water all of the garden?

(Round your answer to two decimal places)

note: i don't know the answer in this one so please answer this with solution(if you can thanks).

Q3: Volume. A flat, square piece of cardboard is used to construct an open box by cutting out squares (measuring 1 foot by 1 foot) from the corners and folding up the resulting edges. If a particular box has a volume of 25 cubic feet, what are the dimensions of the original piece of cardboard?

note: the answer should be this: The dimensions of the original piece of cardboard are _______ feet by ______ feet. all you need to do is give the solution and the answer in a ANSWER feet by ANSWER feet. in the question (1 foot by 1 foot) thanks for understanding.

thank a lot everyone, have a nice day.

1. 19 & 21

(2n+1)(2n+3)=399
4n^2+8n+3=399
4n^2+8n=396
n^2+2n=99
n^2+2n-99=0

the quadratic formula (-b+-sqrt(b^2-4ac))/2a
a=1 b=2 c=-99
-2+-sqrt(2^2-4(1)(-99)/2(1)
-2+-sqrt(4-(-396))/2
-2+-sqrt(400)/2
(-2+-20)/2
(-2+20)/2 & (-2-20)/2
9 & -11 = n
**only 9 works because you cannot have a negative number so you know that -11 you can toss out!

then you have to remember that the odd number formula is:
2n+1 & 2n+3
so you plug in 9 and 11 and get 2(9)+1 & 2(9)+3
therefore the numbers are 19 and 21

2. 29.698

The reason why I think this is the answer is because a square garden with 1764ft^2 has sides measuring 42ft. So the smallest radius the circle could have would have to be half of the diagonal as the smallest radius. So I said half of the sides equaled 21 so I did the diagonal formula for it which was sort(21^2+21^2)=sqrt882=29.698