Answer:
(a): 10 civil servants who were absent.
(b): 15 civil servants are in field only.
Explanation:
Let;
- Civil servants in office be o
- Civil servants in field be f
![{ \rm{ \sum(n) = 90}} \\ \\ { \rm{n(o) = 65}} \\ \\ { \rm{n(f) = 50}} \\ \\ { \rm{(o \: { \huge{n}} \: f) = 35}}](https://img.qammunity.org/2022/formulas/mathematics/high-school/uolxhctch71zfx6e7u7x5zphbanvnz776o.png)
Question (a):
Let the absentees be x
![{ \rm{x + (65 - 35) + (50 - 35) + 35 = 90}} \\ \\ { \rm{x + 80 = 90}} \\ \\ { \rm{x = 10}}](https://img.qammunity.org/2022/formulas/mathematics/high-school/4bopsk02p7ozh9eoeryy13r5mf1jax89p0.png)
There are 10 absentees.
Question (b):
Servants in field only;
![{ \rm{n(f \: only) = 50 - 35}} \\ \\ { \rm{n(f \: only) = 15 \: servants}}](https://img.qammunity.org/2022/formulas/mathematics/high-school/l0r6jrj00drnuxathfza2t4ahq1g4ky90r.png)