Hi Newaz111,
This is an example of a 'Symbolism' question; in these types of prompts, you are given a 'made up' math symbol, told what it 'means' mathematically, then you're asked to perform some calculation using it. The math involved in these types of prompts is usually basic arithmetic or algebra, so you just have to stay organized and follow the instructions that you're given.
For the purposes of simplifying the visuals, I'm going to use the $ symbol as the 'symbol' for this question...
We're told that X$Y = (X-Y)/(X+Y)
Next, we're told that 3$Y = 5$4.....so let's set up these calculations using the symbol we've been given...
(3-Y)/(3+Y) = (5-4)/(5+4)
(3-Y)/(3+Y) = 1/9
Now we can cross-multiply....
27 - 9Y = 3 + Y
24 = 10Y
24/10 = Y
12/5 = Y
Final Answer: D
GMAT assassins aren't born, they're made,
Rich
