Find the $G$.$C$.$D$. of $(28, 35, 91)$.

The length,breadth,and height of a prayer room are $15\,m$,$12\,m$,and $21\,m$ respectively. Determine the longest rod which can measure the three dimensions of the room exactly. (in $,m$)

Find the smallest five-digit number which is exactly divisible by $15$,$55$,and $99$.

Prove that $8^{n}$ cannot end in zero for any natural number $n \in N$.

Four bells toll at intervals of $8$,$12$,$15$,and $18$ seconds respectively. All four begin to toll together. How many times will they toll together in one hour,excluding the one at the start?

State whether the following rational number has a terminating decimal expansion or not. If it has,then find it: $\frac{9}{30}$