Correct Answer: 7 – 543

Solution : Taking the cube of the first number and reversing the digits to obtain the second number.

First option: 6 – 612→6 ³ = 216; On reversing the digits, 216 becomes 612.
Second option: 5 – 521→5 ³ = 125; On reversing the digits, 125 becomes 521.
Third option: 4 – 46→4 ³ = 64; On reversing the digits, 64 becomes 46.
Fourth option: 7 – 543→7 ³ = 343; On reversing the digits, 343 remains the same not become 543.

So, the fourth option is different from the other three options as the second number is not the reversed digits of the cube of the first number. Hence, the fourth option is correct.