AECD is a parallelogram but I don’t get it
Subtract 4 from both sides of the equation
you will end up with 2/7x=4
next multiply 7x by both sides
you will end up with 2=28x
next divide 28 from both sides
you will end up with x=1/14 in
fraction form. Hope this helps.

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
:



I do not see anything wrong with it
There are 730 total boxes. The last box has 108 toys.