This isn't exactly a tricky question. Rewrite the molecules on some paper and you will see the difference. You know the more internal a double bond (or substituted) is then the major product. Kaplan just drew the 2 molecules in different ways.
Once you protonate the alcholol it leaves and you get a carbocation that looks like this
CH2CH2CH3 (Sorry can draw it out better it doesnt let you skip spaces)
There are 2 ethyl groups and a propyl group and we have a choice which H to remove to form the double bond. Thats how they got the 2 products.
To form the double bond in the top answer you remove a hydrogen from one of the ethyl groups.
To form the double bond which is major you remove a hydrogen from the propyl group on the bottom and this double bond is more internal as Doc said and that makes it major (the top one has only a methyl group to the left of the double bond so its closer to the end of the molecule but in the bottom one the double bond has ethyls on all sides ie is more internal
((yes there is a Hydrogen on the double bond but its there on both just not written out as clearly in the first one))