If \(x\) and \(y\) are distinct positive integers and \(x+y\) is even, what is the remainder when \((x+y)^a\) is divided

[VJesus12]

If \(x\) and \(y\) are distinct positive integers and \(x+y\) is even, what is the remainder when \((x+y)^a\) is divided by \(10,\) where \(a\) is a positive integer?

(1) Units digit of \(y\) is \(6.\)
(2) \((xy)^a\) is divisible by \(10.\)

Answer: C

Source: e-GMAT