A project involves eight activities with the precedence relationship and duration as shown in the table below. The slack for the activity D is __________hours (answer in integer).
$$ \begin{array}{|c|c|c|} \hline \text { Activity } & \text { Immediate predecessor } & \text { Duration(hours) } \\ \hline A & - & 4 \\ \hline B & A & 8 \\ \hline C & A & 5 \\ \hline D & B & 2 \\ \hline E & B & 7 \\ \hline F & C & 6 \\ \hline G & D & 3 \\ \hline H & E, F, G & 9 \\ \hline \end{array} $$The endurance limit of a specific grade of steel is same as its yield strength. The ultimate strength of this grade of steel is twice of its yield strength. A component made of this steel is loaded in tension and unloaded periodically. It is required that the component does NOT fail for at least $10^6$ loading cycles, as per the Soderberg law. Considering a factor of safety of 2 , the maximum applied tensile principal stress is
A pair of spur gears is required to maintain a velocity ratio of $1: 2$. The module of the gears is 10 mm and the addendum is 10 mm . If the operating pressure angle is $15^{\circ}$, the minimum number of teeth required on the pinion to ensure NO interference/undercutting is _________ (answer in integer).