The question has to be "Which of the following cannot be the value of m?"

You can quickly check from the options and it will be 24.

80 divided by 24, the remainder is 8 and 24-8 is not equal to 16.

So 24 is the answer....

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Here is the conceptual approach

80 = km + n = km +m-4
84= m(k+1)

Hence m must be a divisor of 84. All the options other than 24 are the divisors of m.

That's a nice explanation sureshbala....I would like to finish this using options