The diagonals of which one of the following geometric figures bisects each other orthogonally?

If the difference between $\angle \mathrm{A}$ and $\angle \mathrm{B} (\angle \mathrm{A}>\angle \mathrm{B})$ of the parallelogram $\mathrm{ABCD}$ be $20°$, then $\angle \mathrm{A}=$

If $\angle A:\angle B=3:1$ in the parallelogram $ABCD$, then $\angle A=$

If the lengths of the diagonals of the rhombus $ABCD$ be $6 \mathrm{cm}$ and $8 \mathrm{cm}$ respectively, then the perimeter of the rhombus is equal to 

The other angles of the parallelogram $ABCD$ if one of its angles is $60°$, are 

The perimeter of a parallelogram is $50 \mathrm{cm}$. If the length of its greater side be $15 \mathrm{cm}$, then the length of its smaller side is equal to  

If in the parallelogram $ABCD, AB=(2x+4) \mathrm{cm}, DC=(4x-12) \mathrm{cm}$ and the length of each of the two other sides of it be $\left(2x-5\right) \mathrm{cm}$, then $\left(2x-5\right)=$