Find the average temperature on that part of the plane 5 x plus 3 y plus z equals 9 over the square startabsolutevalue x endabsolutevalue less than or equals 1, startabsolutevalue y endabsolutevalue less than or equals 1, where the temperature is given by upper t (x comma y comma z )equalse superscript negative z. the average value is nothing. (type an exact answer, using radicals as needed.)