Calculate with a calculator. Give the answers at the accuracy of three digits.

a) [[$ \sqrt {11} – \sqrt {6 – 2} = $]]

b) [[$ \sqrt {5} \cdot \sqrt {9 + 12} = $]]

c) [[$ \sqrt {13} : 13 = $]]

d) [[$ 1 – 2 \cdot \sqrt {3} = $]]