Need help with these questions, I have found the answers for one part but need help with part 2

The median weight of a boy whose age is between 0 and 36 months can be approximated by the function w(t) = 9.58 + 1.46t - 0.001 1t + 0.00042713, where t is measured in months and w is measured in pounds. Use this approximation to find the following for a boy with median weight in parts a) and b) below. a) The weight of the baby at age 7 months. The approximate weight of the baby at age 7 months is 19.89 lbs. (Round to two decimal places as needed.) b) The rate of change of the baby's weight with respect to time at age 7 months. The rate of change for the baby's weight with respect to time at age 7 months is approximately Ibs/month. (Round to two decimal places as needed.)