We are given in the question that:

We are meant to calculate the number of gallons that will fill the entire bin, such that we can have:

We know that the ratio of both expressions will give the same value, therefore, the equation that can be used to solve will be:

We can further solve to get the amount of water by cross-multiplying:

Solving, we have:

Therefore, it will take 3/8 gallons to fill the bin.