I don't understand question 17

For qn 17 part a

Since we do not know how much Mr Singh has borrowed, we let it be $x

Since the interest is compounded annually,

First year:

($x)(10/100)(1) = 0.1x ( This is the interest for the first year)

We need to add them to the amount at the start which is $x

So end of first year, the amount build up will be $c + 0.1x = 1.1x.

For part a

Do the same for the 2nd and third year. At the end of the third year the equation in x should amount to $10 648

Solve for x then

For part b

Since he borrowed $8000 and the total amount payable is $10 648, the qn wants you to find how long will it take to pay back the interest. Thats why we need to subtract the two values and get the number of year using the simple interest formula (PRT=I) where now the time is the unknown