Four of them.
A rectangle has four corners, each of which is 90 degrees. 4 * 90 degrees = 360 degrees
If it weren't 90 degrees it wouldn't be a rectangle. Are you sure you worded this the way you meant?
A rectangle, by definition, has four angles, each of 90 degrees.
Both a square and a rectangle have 4 angles of 90 degrees.
A square and a rectangle
All angles of a rectangle are 90 degrees.
90 degrees
90+90+90+90
Each angle of a rectangle measures 90 degrees.
A right angle - whether or not in a rectangle - is 90 degrees.
The corner of a square or rectangle is 90 degrees.
90 degrees