Correct Answer: 45

Solution : Given:
324 @ 289 = 35, 441 @ 484 = 43

The sum of the square root of the L.H.S. equals R.H.S. of the given equation.
Like, 324 @ 289 = 35 –
The square root of 324 = 18 and the square root of 289 = 17
So, 18 + 17 = 35
And, 441 @ 484 = 43 –
The square root of 441 = 21 and the square root of 484 = 22
So, 21 + 22 = 43
Similarly, follow the same pattern for 25 @ 400 –
The square root of 625 = 25 and the square root of 400 = 20
So, 25 + 20 = 45

Hence, the first option is correct.