First lets convert both X and Y to Standard normal distribution.
Z=X-1/2
Z=Y+1/σ
Now replace X and Y in P(X<=-1)=P(Y>=2) we get P(Z<=-1)=P(Z>=3/σ)
Since the Standard Normal Curve is symmetric about the mean( i.e, zero) -(-1)=3/σ⟹σ = 3.
Answer is Option A