"Translation by vector B" just adds vector B: X= tP+ sQ+ B.

To "rotate through angle [itex]\theta[/itex] around the point C"

i) Subtract C so you are rotating around C.

ii) Multiply by the matrix

iii) Add C to move back.

In particular, a rotation by 180 degrees, that matrix is , just multiplying x and y by -1.

A rotation by 90 degrees is given by