How many such pairs of letters are there in the word

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

198 + 105 - 215 = ?

If √3ⁿ 729, then the value of n is equal to:

(1296)  ^-3/4  = ?

Find the simplified value of the given expression:

{16 of 13 - 7² + √441 - (3/4) X 64} ÷ (102 ÷ 17)

Find the value of ‘x’ if (5 × 196 – 340 ÷ 17) ÷ 20 = √1600 – x.

[490 of 7 - (13)² of 5] - 1228 = ?

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

(24 ² – 16 ² ) + 75% of 40% of 480 = ?

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

? = 12.5% of 25% of 20% of 1280 + 1248