Here it is given that is divisible by 3.

We know that if a number is divisible by 3, then sum of digits must be a multiple of 3.

∴ 1 + 8+x+7+1 = multiple of 3

∴ a + 17 = 0,3,6,9,12,15,…..

But ‘x’ is a digit, hence, ‘x’ can have value between 0 to 9.

∴ x + 17 = 18 which gives x = 1.

∴ x+ 17 = 21 which gives x = 4.

∴ x + 17 = 24 which gives x = 7.

∴ x = 1,4,7