if f(x)=3x and g(x)=1/3x, which expression could be used to verify that g(x) is the inverse of f(x)

a. 3x (x/3) ---> already tried this. it's wrong
b. (1/3x)(3x)
c. 1/3 (3x)
d. 1/3 (1/3x)
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