How to solve it
Finish the top row first, then the next one. Once two rows are done, the rest is a smaller puzzle. The last two tiles of a row go in together: park the last one below, line up the pair, then slide them in.
A bit of history
The 4×4 fifteen puzzle appeared in the United States in the 1870s and became a craze around 1880. Half of all random arrangements can never be solved, so Comma Puzzles shuffles by making real moves from the solved state. Every board is solvable.