Units digit questions are all about patterns.As we are asked about units digit so we need to focus only on units digits of the numbers in equation and we need to find out the pattern that repeats after a certain set of numbers.Therefore,we are only concerned with 6 in 286 and the 2 in 52.
So our new equation should be $6^1^0-2^1^2 = n$ and we should look for patterns.

Now consider 6 for pattern :

$6^1 = 6$
$6^2 = 36$
$6^3 = 216$
$6^4 = 1296$
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It may be noted that no matter to what power you raise a number with a 6 as its units digit, the units digit will always be 6

Now consider 2 for pattern :

$2^1 = 2$
$2^2 = 4$
$2^3 = 8$
$2^4 = 16$
$2^5 = 32$
$2^6 = 64$
$2^7 = 128$
$2^8 = 512$
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It may be noted that at $2^5$ the pattern starts over again.So our units digit pattern for 2 is 2,4,8,6

So $286^1^0-52^1^2 = n$ => $6^1^0-2^1^2 = n$ => $6-6 = n$ => $n = 0$.
=> the units digit of n is 0,therefore answer is C i.e. Quantity A = Quantity B

This question has been taken from tests of Greatest Prep.Here is the link to the website of Greatest Prep : http://www.greatestprep.com