First, we get the area of the whole rectangle, easy enough:
18 * 16 = 288 cm²
Now, for the area of the circle, we use the circle area formula:
Area = pi * r²
Area = 3.14 * 6² = 3.14 * 36 = 113.04cm²
Now we substract the circle area from the rectangle area:
Shaded region = 288 - 113.04 = 174.96cm²