I've seen a lot of 500+ word answers on here, and not I don't think that's a bad thing at all, but for most of the answers, the point isn't conveyed until halfway through the answer.

Simply put, *began* and *spending* are a Verb+Infinite pair, in which 2 verbs are used one after another to convey additional information.
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> Why?

In this pair, *began* is the infinitive verb and *spending* is the base verb.
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We know this because if we remove *began* and change the tense of *spending* to *spent*, the sentence still conveys the same point but with less detail

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Sources:

[Business English Resources](http://www.businessenglishresources.com/31-2/student-section/student-handouts/infinitive-vs-gerund-combining-two-verbs/)

[University of WA](http://staff.washington.edu/marynell/grammar/infini.html)

[EnglishPage.com](http://www.englishpage.com/gerunds/)