The three slices are each approximately 1/9 pound in weight, and, since 2/9 is less than 1/4, he can eat 2 whole slices and be okay. If he wants to eat partial slices, then he could eat 2 1/4 slices, as each slice weighs 4/36 pounds, so 2 slices would equal 8/36 pounds, leaving 1/36 pound left over in his diet, which is a quarter of the third slice.
2.25