This is very sloppy but u hope it helps
we have that
the total cost is

In this equation the term 30h represent the cost due to h hours at at unit of 30
and the term 0.040(30h) is equal to calculate the 4% of (30h)
so
in this problem the tax rate is equal to 4%
therefore
<u>the answer is</u>
The term 0.040(30h) represents the amount of tax she must pay
it equals to -2+10v since you have to distribute the -2 to the 1 and -5v