



 
Hi Heather, The volume of the sponge is given by V = V(t) = LWH where L = L(t) is the length in cm, W = W(t) is the width in cm, H = H(t) is the height in cm and t is the time in minutes. Differentiate both sides of
V(t) with respect to t to obtain an expression of the form
Substitute the values you are given for the right side at the given time to find V'(t) at this time. Now write the surface area as a function of L, W and H and apply the same technique. If you have any difficulty completing this just write back and tell us what you have done and we will try to help. Penny  


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