Hello! I shall do part (a) first...
Have you learnt Cosine Rule?
Basically Cosine Rule states that (in the context of this question):
Therefore, by applying Cosine Rule, we can find AC:
[rounded off to 5 significant figures] = 11.2 cm [rounded off to 3 significant figures]
Okay now for part (b)...
The formula for area of triangle is (in the context of the question):
Area of triangle ABC
In general, the formula is Area of triangle , where a and b are adjacent sides of a triangle and C is the angle opposite side c (i.e. the angle between sides a and b).
By applying this formula, we can answer the question:
Area of triangle ABC = = (rounded off to 3 significant figures)
Hope this helps! ^^