At around 20'000ft. and higher.
A(b-c)=ab-ac
(1/7)(1/3h-1/2)=(1/7)(1/3h)-(1/7)(1/2)=1/21h-1/14
now we gots
6 and 1/7+1/21h-1/14
rearange
6 and 1/7-1/14+1/21h
make common denom which is 14
6 and 2/14-1/14+1/21h
6 and 1/14+1/21h

First, we need to find how much a single pound of apples costs.
Do this by dividing.

Now, write an equation.

This represents that the cost equals 3.5 times the number of apples.