i don't know how i am supposed to calculate the three last columns of the table for my thin lens lab

C. With measurements Start with the object as far as possible from the lens and move it closer to the lens until a sharp image of the object is projected on the screen. To find the object's location giving the sharpest image, move the object back and forth. Measure the distance do from the object to the lens. Repeat this twice and record do, mend hr in Table 1. For each of them, calculate the average, absolute and relative uncertainty. Note whether the image is inverted or not. Table 1:d-= 50 cm, step 3. Values are in cm. 1 2 3 Average Am; .5153,\" e[%] do, 20.2 cm 21.0 cm 21.3 cm 20.8 cm m 6.3 cm 719 cm 7.? cm 7.3 cm hi 8.0 cm 6.1 cm 6.0 cm 6.7 cm