TS EAMCET 2017 Code A Solved Paper

Consider the given function.
f(x)=−3x−3
Substitute 3 for f(x)
−3x−3=3
−3x=6
x=−2
Substitute -6 for f(x)
−3x−3=−6
−3x=−3
x=1
Substitute -9 for f(x)
−3x−3=−9
−3x=−6
x=2
Substitute -18 for f(x)
−3x−3=−18
−3x=−15
x=5
Therefore, the domain of the function is
f={−2,1,2,5}