You have four states in which RetailCo is active, and its RMS for each state is given below the mosaic plot (2.1, 0.8, 0.9 and 0.6). You can quickly confirm that these numbers are correct using the provided formula. Now, you need to calculate the overall RMS from the RMS values given for each state. Because the markets of the different states are not of the same size, you cannot calculate a simple average and be done with it, but need to calculate the weighted average, with the size of each of the markets ($2.3, $1.7, $1.4 and $1.0) being the weighting factor and the divisor being the total market size ($6.4). So the calculation you need to do is:
(2.1x2.3 + 0.8x1.7 + 0.9x1.4 + 0.6x1) / 6.4 = 1.26
This gives 1.2 as the closest answer. Hope this is correct and helps you out!