Divide the shape to two different shapes
We get a trapezium/trapezoid
And a triangle
Formula of the area of a trapezium:

× height × (base₁ + base₂)

× 5 × (14 + 18)
*(height is 5, because 17 - 12 = 5)
2.5 × 32
80 mm²
Formula of the area of a triangle:

× base × height

× 18 × 12
48 mm²
Total Area:
Area of trapezium + Area of triangle
80 + 48
128 mm²