The first section on the bottom row of your calculation sheet covers the calculations required for the capability index Cp. As discussed in the section on capability, this index tells you whether the natural process spread could be contained within the customer's specified limits. The first stage is to find the natural process spread, which is the distance between the upper and lower control limits, or 6 sigma units (6s).
The values for UCL X and LCL X which you have already calculated in the previous exercise have been entered into the first two boxes. Complete the calculation for the value of 6s, enter your answer in the box outlined in red, and then click the button to check your answer.