The total wingspan for data set **A** is 6 x 13 =
78 cm so the missing measurement is 78 - 67 = 11 cm.

The total wingspan for data set **B** is 7 x 14 =
98 cm so the missing measurement is 98 - 84 = 14 cm.

The overall mean is 13.35 cm so the total of all 20 measurements
is 20 x 13.35 = 267 cm and the total wingspan for data set
**C** is 267 - (78 + 98) = 91 cm.

The missing measurement for data set **C** is 91 -
76 = 15 cm and the mean of data set **C** is 91/7 = 13
cm.