Note: Rhombus is not drawn to scale.

For b) pq/2 is the formula for the area of a rhombus where p = diagonal 1 and q= diagonal 2

The second answer for b) follows the idea that a diagonal line within a rhombus dissects it into two identical triangles. To find the area of 1 triangle: [length (48) x height (a)] / 2

The detailed working for the second answer to b would thus be:
Area of triangle = (48 x 46.13025) / 2 = 1107.126
Area of rhombus = 2 x 1107.126 = 2214.252 = 2210 (3s.f.)

The working in the photo has been simplified since the two steps cancel each other out.