1.75: Trigonometric equations and geometry

In triangle $ABC$, $AB=10$ cm, $BC=7$ cm and angle $BAC=40^\circ$.

(a) Find, in degrees to the nearest $0.1^\circ$, the two possible sizes of angle $ACB$. (4)

(b) Find, in cm to 3 significant figures, the difference between the two possible lengths of $AC$. (4)