Given the Partial Project Network Below and the Fact That $\ge$

Essay

Given the partial project network below and the fact that F can be crashed three times if X_t = start time of Activity i, and Y_i = amount of crash time used for Activity i.
a.Which of the following is correct?
X_F $\ge$ X_D + 10 - Y_D or X_F $\ge$ X_E + 10 + Y_E or Y_D, Y_E $\le$ 0 or X_F - X_D - X_E + 10 $\ge$ 3
b.Which of the following is correct?
y_D $\le$ 3 or y_E $\le$ 3 or y_F = y_D + y_E or y_F $\le$ 3