\(75883-\left(31200+a\right)=999\)
\(\Rightarrow75883-31200-a=999\)
\(\Rightarrow44683-a=999\)
\(\Rightarrow a=44683-999\)
\(\Rightarrow a=43684\)
Vậy a=43684
75883-(31200+a)=999
31200+a =75883-999
31200+a =74884
a=74884-31200
a =43684
Vậy a = 43684