Just like a sentence needs punctuation, math equations need parenthesis. I kinda hate these internet puzzles that are really just examples of how not to do math.
Twenty five dollar bills - is that $100 or $25?
Twenty, five dollar bills = $100
Twenty five, dollar bills = $25
TO OP - 4 is the right answer for how it is written, but is that what was intended? That's where Engineering judgement comes in, and where a set of parenthesis would have gone a long way.