Since sales tax goes after the discount, it would be 3 dollars and 20 cents. Taking 50 dollars and 20% is discounted (50*.2), which would be 10 dollars taken off. It would be 40 dollars shoes and then you apply sales tax by multiplying 40 by .08, giving you the amount of tax paid.
We can write the system in the following form:
![\left[\begin{array}{cccc}5&-4&4&2\end{array}\right] \left[\begin{array}{c}x_1\\x_2\\x_3\\x_4\end{array}\right] =b](https://tex.z-dn.net/?f=%20%20%5Cleft%5B%5Cbegin%7Barray%7D%7Bcccc%7D5%26-4%264%262%5Cend%7Barray%7D%5Cright%5D%20%20%5Cleft%5B%5Cbegin%7Barray%7D%7Bc%7Dx_1%5C%5Cx_2%5C%5Cx_3%5C%5Cx_4%5Cend%7Barray%7D%5Cright%5D%20%20%3Db)
The above system is equivalent to the following equation:

Of course, the above system has solution for any values of b since there is one equation and four variable, there is infinite number of solution each time.
20/10 as a mixed number:
20 ÷ 10 = 2.
10 goes into 20 two times. So 20/10 as a mixed number is a whole number: 2.
20/10 = 2