The trick to calculating the area here is to subdivide the diagram into smaller parts. For example, there's a 3 cm-by-3cm square. The rectangle is 4 cm by 8 cm.. The triangle has a base of 5 cm and a height of 3 cm.
Total area = area of square + area of rectangle + area of triangle
= 9 cm^2 + 32 cm^2 + (1/2)(5 cm)(3 cm)
= (9 + 32 + 7.5) cm^2
= 48.5 cm^2 (total area of figure)