Dual energy subtraction for X-ray imaging involves subtracting one image from another after both images have been appropriately scaled as follows: Image3 = a x Image 1 - bx Image2 = where a= 0.2 and b=0.3. A pixel in Image1 and Image2 has expected values of 200 and 120, respectively, for the measured photons counts. For that pixel in Image3, compute the: 1) Variance 2) Expected value 3) Relative standard deviation