Sarah borrowed $100,000 at 8% for 10 years on January 1, 2020 from a local bank

The initial loan was taken for 100,000

For the first 5 yrs , the loan has been paid back the interest only

So the Interest for each year = 100,000 * 8% = 8000 per year

Total interest for 5 Year (INTEREST 1) = 5 * 8000 = 40,000

Now the loan is amortized for both principal and interest for the remaining 5 years

So the

Amortization payments

payment = P*(i)   / ( 1- (1+i) ^–t

Where p = principal

I = interest rate

T = time

payment = P*(i/m)   / ( 1- (1+i/m) ^–mt   = 100,000 *(0.08) /1-(1+0.08)^-5 = 25,045.65

So the Yearly payment are = $ 25,045.65

Total instalment paid on the loan = 25045.65 * 5 = 125,228.23

So the interest part is = 125,228.23 – 100,000 = 25,228.23

Hence to total interest paid is = Lat 5 yrs interest + First 5 yrs interest = 25,228.23 + 40,000 = 65,228.23