。
She solved the puzzle easily.
Literal
She [topic-は] that puzzle [object-を] easily solved.
解く covers a wide span: solve a puzzle, untie a knot, cancel a contract, dispel a misunderstanding — all sense the original meaning of 'unravel'. The common kanji compound 解決する ('solve, resolve') extends the same root. 簡単に ('easily, simply') uses に to turn the na-adjective 簡単 into an adverb — に for na-adjectives parallels く for i-adjectives. パズル is a katakana loanword that fits the modern leisure puzzle (jigsaw, sudoku, crossword) more than abstract math problems, which would attract 問題.