Setting equal height of label


#1

The book asked to set both the nameLabel and serialNumberLabel to equal and says that there will be an unsatisfiable constraint and showed this Visual Format language as an interpretation of the auto layout i set
“V:|-1-[nameLabel(==21)]-5-[serialNumberLabel(==15)]-1-|”

How could this be true that nameLabel has 21 points height and serialNumberLabel has 15 points height when i set both of the height to be equal. I don’t understand this part of the book.