Today, isaac needs to walk his dog, water the garden, and feed his fish. d is the number of minutes it takes to walk his dog, g is the number of minutes it takes to water the garden, and f is the number of minutes it takes to feed his fish. the expression g+(d+f) describes the total number of minutes it takes issac to do all three task. we can also use the expression (g+d)+f to represent the same quanity