Step-by-step explanation:
Draw a picture (like the image below).
Notice that triangles ABC and ACD both contain right angles, and both contain angle A (20°). Since angles of a triangle add up to 180°, that means their third angle must also be the same (70°).
Also notice that triangles ABC and CBD both contain right angles, and both contain angle B (70°). So their third angle must also be the same (20°).
Therefore:
m∠CDB = 90°
m∠CBD = 70°
m∠BCD = 20°
m∠CDA = 90°
m∠CAD = 20°
m∠ACD = 70°
