"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