We have,
sinθ=cos(θ−6o)
⇒cos(90o−θ)=cos(θ−6o)
Now, Comparing that,
(90o−θ)=(θ−6o)
⇒90o+6o=2θ
⇒2θ=96o
⇒θ=48o
Hence, this is the answer.