I m not sure about my method, but let me try it.

i assume that u know about this formula:
(F U R) = (F) + (R) - (F n R)

Let total no of diplomat = X
so (F U R) = 0.8X ==> as 20% can not speak either
(F n R) = 0.1X ==> 10% can speak both

(R) = X - 32 ==> 32 can not speak Russian
(F) = 20

so
0.8X = 20 + X - 32 -0.1X
0.8X = 0.9X - 12
X ==> 120

I approached this way

20 - speak french
32 - don't speak russian mean this is lot of diplomats speaking both french n russian, but we've 20 as french so rest 12 = 10% is diplomats speaking both languages so 120 = total diplomats