What is the chemical formula of rust?

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

?² - 22² = 900 ÷ 4 - √1089

If (i) P is taller than Q, (ii) R is shorter than P, (iii) S is taller than T but shorter than Q, then who among them is the tallest?

{(700 ÷ 20) × 40} – 30 × 18 = ?% of 1000

If x²- 5x + 1 = 0, what is the value of x² + 1/x²?

45% of 1020 + ?% of 960 = 747

154 × 7 + 480 × 5 = ?% of 6956

√? × 4 - 374 + 127 + 300 = 117

12/15 of 13/60 of 7/39 of 90603 = ?

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

41² + 25% of 2400 = ? + 1131