$$7 sin^{2} θ + 3 cos^{2} θ = 4$$
$$\rightarrow7 sin^{2} θ + 3 - 3sin^{2} θ = 4$$
$$\rightarrow4 sin^{2} θ = 1$$
$$\rightarrow$$sin θ = $$\pm\frac{1}{2}$$
but (0° < θ < 90°) so θ = 30
then tan θ = tan30 = $$\frac{1}{\sqrt{3}}$$
so the answer is option A.
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