From geometry of figure In
\(\Delta ABC; \alpha = 180° -(60° + 40°) = 80°\)
==> \(\beta = 90° -80° = 10°\)
In \(\Delta ABD; \angle A = 60°, \angle B = (\alpha + 2\beta)\)
= \((80 + 2 \times 10) = 100° and \angle D = (90° -\theta)\)
\(\because\) \(\angle A + \angle B + \angle D =180°\)
\(==> 60° + 100° + (90° -\theta) = 180° ==> \theta = 70°\)