Here, AB is the chimney, CD the observer and ∠ADE the angle of elevation (see Fig.).In this case, ADE is a triangle, right-angled at E and we are required to find the height of the chimney.We haveAB=AE+BE=AE+1.5and DE=CB=28.5 mTo determine AE, we choose a trigonometric ratio, which involves both AE and DE. Let us choose the tangent of the angle of elevation.Now,tan45∘=DEAE​i.e.,1=28.5AE​Therefore, AE=28.5So the height of the chimney (AB)=(28.5+1.5)m=30 m.