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Explanation:

For various powers the units digit of a number always a cycle of 4 terms.

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We need unit’s digits of (X)63 and (Y)85 to be same

Unit’s digit of X63 will be same as unit’s digit of X3
Similarly, unit’s digit of Y85 is same as unit’s digit of Y1.

∴ unit’s digits of (X)3 should be same as units digit of Y.

This is possible (from the table) when (X, Y) = (2, 8) or (8, 2) or (7, 3) or (3, 7).

In any of these cases X + Y = 10.

Hence, option (b).

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