Which of the following is irrational?

Irrational numbers are numbers that cannot be expressed as the ratio of two whole numbers. This is opposed to rational numbers, like 2, 7, one-fifth and -13/9, which can be, and are, expressed as the ratio of two whole numbers.

For this case we have the following expression:
 24 + 56
 The factors of the numbers are:
 24: 1, 2, 3, 4, 6, 8, 12, 24
 56: 1, 2, 4, 7, 8, 14, 28, 56
 So, factoring we have:
 24 + 56 = 8 (3 + 7)
 Simone wrote:
 24 + 56 = 8 (4 + 7)
 Therefore his error is:
 Simone did not use the correct factors for 24 in the equation
 
 Simone did not use the correct factors for 24 in the equation