A. Expanding the given expression, you have
balance = 75r^2 +150r +75
B. For r=0.10, the balance after 2 years is 75*1.1^2 = 90.75
C. The difference between $120 and 90.75 is $29.25. You need $29.25 more to buy the bicycle.
13. 10-14
14.I can't see the whole graph, so you need to do it yourself. Add up everyone's age and divide by the amount of people on the graph. That will give you the average.

Divide both sides by
to get


Substitute
, so that
. Then



The remaining ODE is separable. Separating the variables gives

Integrate both sides. On the left, split up the integrand into partial fractions.




Then

On the right, we have

Solving for
explicitly is unlikely to succeed, so we leave the solution in implicit form,

and finally solve in terms of
by replacing
:


