hi zee-f
For the first, I cannot see what answer you chose.
Did you work out the width first ?
For Q18, start by making a drawing on paper. It doesn't have to be accurate, just make it look roughly like the given drawing.
Then mark on all the distances.
Split the shape into rectangles. There's more than one way of doing this step. I've shown one way on my diagram.
Using the length and width* for each rectangle, write down its area.
Add them up and you're done.
* You might have to do some adding or subtracting to work out the distances you need.
Bob