Mathematics
Answer
From figure,
∠DAC = 180° - 138° = 42°.
∠BDC = 180° - ∠ADC = 180° - 116° = 64°.
In △BCD,
∠CBD = ∠BDC = 64°.
∠DCB = 180° - (∠CBD + ∠BDC) = 180° - (64° + 64°)
= 180° - 128° = 52°.
In △ADC,
∠DCA = 180° - (∠CAD + ∠ADC) = 180° - (42° + 116°)
= 180° - 158° = 22°.
From figure,
∠ACB = ∠DCB + ∠DCA = 52° + 22° = 74°.
Hence, ∠ACB = 74°.