5 is subscript and 3 is superscript.

3.24m=240dm 5m=50dm

S=240*50÷2=6000 (square decimeter)

Potatoes can be planted: 6000÷20=300 (tree)

4. 1, 14 ships

2, 2 big boats, 9 small boats

3, 4 big boats, 4 small boats