First find the difference between the total payment and what the payment would have been prior to to the 20 days late fee. Divide that number by the amount of days overdue (20) to find the cost of each day overdue. Divide that number of what each day overdue is by the cost of the bill prior to overdue fees. Move the decimal two places to the right.
All the 5 rows of the coefficient matrix (since it is of order 5×8) will have a pivot position. The augmented matrix obtained by adding a last column of constant terms to the 8 columns of the coefficient matrix will have nine columns and will not have a row of the form [0 0 0 0 0 0 0 0 1]. So the system is consistent.
