The price of the stove = $850
The payment down = $127.50
We will subtract 127.50 from 850 to find the rest amount should be paid
850 - 127.50 = $722.5
The remainder = $722.50
The value of each installment = $46.79
For 18 month
The amount of installments = 18 * 46.79 = $842.22
the finance charge is the difference between the total installments and the remainder
Finance charge = 842.22 - 722.50 = $119.72
The finance charge is $119.72