If
w^(')(t)
is the rate of growth of a child in pounds per year, what does
\int_6^9 w^(')(t)dt
represent? The child's weight at age 6. The change in the child's weight (in pounds) between the ages of 6 and 9 . The child's weight at age 9. The child's initial weight at birth. The change in the child's age (in years) between the ages of 6 and 9 .