Explanation:
let's simplify the situation.
the balloons are all round and can only touch each other with wide gaps between them.
we use these gaps and add them to the balloons making them cubes instead of spheres.
filing up the gaps with now cubic balloons does not change the number of balloons.
so, each cubic balloon has a side length of 2×0.35 = 0.7 ft, as 0.34 ft is only the radius (half the diameter or side length).
the volume of such a cubic balloon is
0.7³ = 0.343 ft³
the volume of the room is
38×52×12 = 23,712 ft³
so, we need 23,712 / 0.343 = 69,131.19534... =
≈ 69,131 balloons
we could use also simplified dimensions of the room :
40×50×10 = 20,000 ft³
and we round the balloon size to 0.3 ft³
20,000 / 3/10 = 20,000 × 10/3 = 200,000/3 =
= 66,666.66666... =
≈ 66,667 balloons