SSC JE Mechanical Engineering 11 Oct 2020 Shift 1 Papers

Number = 397801
Prime digits in the number = 3, 7
Composite digits in the number = 8, 9
Difference = (Sum of composite digits) - (Sum of prime digits)
= (8 + 9) - (3 + 7)
= 17 - 10
= 7
Hence, "7" is the correct answer.