£11000 of 3.9% compound interest of 3 years ?

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.