In rhombus $ABCD$,$\angle A = \angle B - 30^{\circ}$,then $\angle C = \ldots$ (in $^{\circ}$)

Angles of a quadrilateral are in the ratio $3:4:4:7$. Find all the angles of the quadrilateral.

$P, Q, R$ and $S$ are respectively the mid-points of the sides $AB, BC, CD$ and $DA$ of a quadrilateral $ABCD$ such that $AC \perp BD$. Prove that $PQRS$ is a rectangle.

$(1)$ $A$ quadrilateral has ......... pairs of consecutive angles.
$(2)$ The sum of measures of all the four angles of a quadrilateral is ...........

In $\Delta ABC$,$P$,$Q$,and $R$ are the midpoints of $AB$,$BC$,and $CA$ respectively. If $AB = 8 \text{ cm}$,$BC = 6.6 \text{ cm}$,and $CA = 5.4 \text{ cm}$,then find the perimeter of $\Delta PQR$ in $\text{cm}$. (in $.0$)

$D$ and $E$ are the mid-points of the sides $AB$ and $AC$ of $\Delta ABC$ and $O$ is any point on side $BC$. $O$ is joined to $A$. If $P$ and $Q$ are the mid-points of $OB$ and $OC$ respectively,then $DEQP$ is