Answer :
since it is a quadrilateral, all the sides will add to 360. If two angles are 90, and one is 99, add them and subtract from 360. The last angle should be 81 degrees.
THE INTERIOR MEASURE OF A QUADRILATERAL IS 360 DEGREES
ADD
90+90+99 AND SUBTRACT THE TOTAL FROM 360
360-279= 81
81 DEGREES IS THE MEASURE OF THE FOURTH ANGLE
HOPE HIS HELPS