Tank problem: What is the rate of flow in the first pipe? If the tank holds g gallons, then the rate of flow should be g/15 gallons per minute. So, what is the rate of flow for the other two pipes.
Now use the formula:
Amount = (rate of flow) x (time) to calculate the time using all 3 pipes. Let time = t and amount = g.
Rectangle to Square problem: The cuts are not straight cuts. Try thinking about the symmetry of the problem. After the two cuts are made, the two pieces are the same size and shape.