Compound Interest
A = P(1 + r)^(n)
A = Amount, r = rate per year = 3.9% = 3.9/100 = 0.039, n = year = 3
A = P(1 + r)^(n)
A = 11000(1 + 0.039)^(3)
A = 11000(1.039)^(3) use calculator
A ≈ 12337.85
Compound Interest = A - P = 12337.85 - 11000 = 1337.85
So at the end of 3 years the Amount is ≈ £12 337.85 and the compound interest is ≈ £1 337.85
Hope this helps.