How many diagonals does each of the following have$?$

$\left(a\right)$ A convex quadrilateral

If the sum of measures of all interior angles of a polygon with $8$ sides is $k°$ then find $k$.

Find the number of sides of a regular polygon in which each exterior angle has a measure of $24°$.

Find the number of sides of a regular polygon in which each exterior angle has a measure of $60°$.

Find the number of sides of a regular polygon in which each exterior angle has a measure of $72°$.