Right, as you mentioned in the comments, you find
by plugging in the different values of
.
For
, we have



Similarly, for
, you get



Answer:
weaker has the heavier of an object
I added individual steps for clarity. Note that g must be positive if the solution is to be real.

Let me know if you have any questions.
Answer:
Therefore the surface area of the balloon is increased at 4 cm³/s.
Explanation:
The balloon is being filled with air at a rate of 10 cm³/s
It means the volume of the balloon is increased at a rate 10 cm³/s.
i.e 
Consider r be the radius of the balloon.
The volume of of a sphere is

Differentiate with respect to t



The surface of area of the balloon is(S) = 

Differentiate with respect to t


Putting the value of


Given that r = 5 cm
=4 cm³/s
Therefore the surface area of the balloon is increased at 4 cm³/s.