A project has four activities $($A$,$ B$,$ C$,$ and D$)$ that must be performed sequentially. The prob$-$ ability distributions for the time required to complete each of the activities are as follows: SELF test ActivityActivity Time$($weeks$)$ ProbabilityA $50\mathrm{.}2560\mathrm{.}3570\mathrm{.}2580\mathrm{.}15$B $30\mathrm{.}2050\mathrm{.}5570\mathrm{.}25$C $100\mathrm{.}10120\mathrm{.}25140\mathrm{.}40160\mathrm{.}20180\mathrm{.}05$