For the cumulative distribution function, find

a$.$ U

$F(x)=\{\begin{array}{cc}0,& x<mn\; id="EditorElement\_2963378">1</mn>\\ 0\mathrm{.}7,& 1x<mn\; id="EditorElement\_2963400">4</mn>\\ 0\mathrm{.}9,& 4x<mn\; id="EditorElement\_2963422">7</mn>\\ U,& 7x\end{array}$

b$.P(x>2)$

c$.)=(6$

d$.P(x=6)$

e$.)=(4$

f$.)=(6$

g$.)=(5\mathrm{.}5$

h$.F(4)$

$f.$ Variance of $U$