f(x) = x − 3, g(x) = x 2
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$$f+g=x-3+x^2 \\\\
f+g=x^2+x-3 \mbox{ where x can be any real number - that is }x\in R$$
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$$f-g=x-3-x^2 \\\\
f-g=-x^2+x-3 \mbox{ where x can be any real number - that is }x\in R$$
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f(x) = x − 3, g(x) = x 2
$$fg=(x-3)x^2 \\\\
fg=x^3-3x^2 \mbox{ where x can be any real number - that is }x\in R$$
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$$f/g=(x-3)/x^2 \\\\
\mbox{x cannot be 0 because you can't divide by 0 so }\\\\\mbox{domain: }x\in R \mbox{ where }x\ne 0$$
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To be honest here I do not see why x cannot be an imaginary number but you probably haven't learned about those yet so these are probably the answers that you need.
+253 
+118608 
