A', A'', A''' means the coordinate where the point A is ending at after the transformation.
A',B' and C' will be after the first transformation (reflection accros the line y=x)
First reflection inverts the points.
A'=(3,1) B'=(1,4) C'=(4,3)
Second transformation, you start from the last points and begin by in every x poisition for every point you should add 5 on every point, and on the y position goes down
A''=(3+5,1-3)
A''=(8,-2) , B''=(6,1) C''=(9,0)
Third transformation, rotation 90° around the origin.
we know that degrees are measured counter-clockwise and 90° will turn the figure sideways.
There is a formula to determine the new position in which
A=(X,Y) A'=(Y,-X)
Apply this to the last points you have.
A'''=(-2,-8) B'''=(1,-6) C'''=(0,-9)