b₄ = 36;

b₆ = 4.

q - ?

b₄ = b₁q³

b₆ = b₁q⁵

frac{ b_{6}}{b_{4}}= frac{b_{1}q^{5}}{b_{1}q^{3}}= q^{2}

q^{2}= frac{4}{36}= frac{1}{9}

q_{1} = sqrt{ frac{1}{9} }= frac{1}{3}

q_{2}=- frac{1}{3}