The general form of a solution of the differential equation is already provided for us:

where
. We now want to find a solution
such that
and
. Therefore, all we need to do is find the constants
and
that satisfy the initial conditions. For the first condition, we have:
For the second condition, we need to find the derivative
first. In this case, we have:

Therefore:

This means that we must solve the following system of equations:

If we add the equations above, we get:

If we now substitute
into either of the equations in the system, we get:

This means that the solution obeying the initial conditions is:

Indeed, we can see that:


which do correspond to the desired initial conditions.
For question 1, We need to calculate the total, find the tax, then add the shipping cost to the total. (70+30+38=138) now we find the tax (138*0.06=8.28) Now we add the tax and cost together and then the shipping and handling and we have our answer (138+8.28+10.75=157.03) So your answer is A.
For question 2, We need to calculate the total and then find the tax. So, we do this: 25.67*3=77.01. Then we add the skirt to the total (77.01+23.55=100.56). Finally, we calculate the tax cost (100.56*0.08=8.0448). So our total is (100.56+8.0448=108.6048) So the answer is A.

If you don't know the first derivative of
, but you do for
and
, you can derive the former via the quotient rule:


or if you know the derivative of
:


As for the second derivative, you can use the power/chain rules:

or if you don't know the derivative of
,


which is the same as the previous result since
