Answer:
total finance cost is 274064
interest in 5 year = 17568.21
creditors reduced in year 8 is 21812.87 
Step-by-step explanation:
given data 
cost = 500000
rate 35% 
installment = 12
annual payment = 49922
to find out 
the total finance cost and interest is charged in 5 year and creditors reduced in year 8 
solution
we know cost is 500000 so down payment will be 
payment = 35% of 500000 = 35/100 × 500000
so payment = 175000
and 12 installment purchase price is 12 ×  49922 
purchase price = 599064
so total finance cost is payment + purchase price - cost
finance cost = 175000 + 599064 - 500000
so total finance cost is 274064
and
we know in 1 to 12 digit sum is 78 
so interest in 5 year 
interest = 5/78 of total finance cost 
interest = 5/78 × 274064
interest in 5 year = 17568.21
and 
interest in 8 year 
interest = 8/78 of total finance cost 
interest = 8/78 × 274064
interest in 8 year = 28109.13
so
creditors reduced in year 8  = 49922- 28109.13 
creditors reduced in year 8 is 21812.87