What is the main chemical used in the production of

What will come in the place of question mark (?) in the given expression?

(20% of 820 – 56 + 11 × 8) ^1/2 = ? – 6²

Solve the following:

240 ÷ 4 × 512 ÷ 8

1365 ÷ 15 + (? ÷ 5) = 6² × 3.5

3% of 842 ÷ 2% of 421 = ?

√10404 + √9604 - ∛1728 - ∛42875 = ?

30% of 215 + 135% of ? = 469.5

(8 x 9) ÷ 5 + ?² = 23.4

The value of (40 + 3/4 of 32) /[37 + 3/4 of (34-6)] is:

{640 of 8 - (12)² of 6} - 900 = ?

`2(1/3)` + `4(1/4)` + `4(2/3)` + `8(7/6)` + ? = `4(3/5)xx4(1/2)`