Calculate and give the answer as a fraction.


a) [[$ \sqrt {1 \displaystyle\frac {9} {16}} = $]]


b) [[$ \sqrt {7 \displaystyle\frac {1} {9}} = $]]


c) [[$ \sqrt {20 \displaystyle\frac {1} {4}} = $]]


d) [[$ \sqrt {2 \displaystyle\frac {7} {9}} = $]]