Answer
a)G
b)f
c)F
d)g
Work Step by Step
a) $y=3x$ is a linear function so it must be G, the only straight line among the graphs.
b) $y=3^{x}$ is an exponential function so it must be f, the only graph which approaches a horizontal asymptote as $x\rightarrow-\infty$ and becomes extremely steep when $x\rightarrow\infty$.
c) $y=x^{3}$ is a cubic (power) function so it must be F.
d) $y=\sqrt[3] x$ is a cubic (root) function so it must be g.