Which function represents g(x), a reflection of f(x) = (3)x across the y-axis?, math homework help

Which function represents g(x), a reflection of f(x) = (3)^x across the y-axis?

g(x) = 2(3)^x

g(x) = −(3)^x

g(x) = (3)^−x

g(x) = 2(3)^−x