This is a volume question so we can use the volume of a cylinder to see which one corresponds to what. Volume of a cylinder is h. We know that the heights of the cylinders are the same since the diagram says so. We also know pi is the same since thats a constant. The only thing thats different is the radius (as you can see radius of P is bigger than Q). If the radius of P is bigger than Q and all the other things are the same (height is the same and pi is the same), then that automatically means that P has more volume than Q. More volume means more time to fill up. Since Q has less volume, it will take less time to fill up. So now we look at the graph. A shows that the height of water increases at a faster rate than that of B. This is because there is less volume in that container (less volume=less time to fill up). Therefore a matches to Q and therefore b matches to P
