Tax= (6/88)
= (3/44) %
Second item = 21(44/3)
= $308
you can see it this way
3/44 is the ideal fraction to calculate tax. The second item requires you to make 21 the tax instead of 3, which you can easily do by multiplying 3 by 7. When you do the same to the 44, you get the price of the second item before tax, which is $308.