Let's evaluate our keywords and translate these words into math so we can create an equation.
Our key word here is <em>of</em>. In mathematics, when we say of, we mean multiplication. For example, when we say, "1/2 of 10", it translates to 1/2 times 10, which equals 10/2 or 5.
Therefore, when we say 1/4 of the total washers (assuming w is the total amount of washers), we mean that 1/4 <em />the total amount of washers represents how many have to be fixed. That would give us:
1/4(w) = 1/4w
As the problem says, the 6 washers that need to be replaced represent the total amount of washers that there are. That means that the 1/4w must equal 6 because that 6 is the amount that is broken.