$a+2b=16$, when $$a=2b=8$$, the largest area is $$8\times (8\div 2)=32$$ m\textsuperscript{2}. 
Farmer Dunphy has $$16$$ metres of fencing.  He wants to make a closed rectangular pen.  He uses a long wall for one of the sides.  Each side of the pen is a whole number in metres.  What is the largest area that the pen can be? 
1. $$25\text{m}^{2}$$ 
2. $$27\text{m}^{2}$$ 
3. $$30\text{m}^{2}$$ 
4. $$28\text{m}^{2}$$ 
5. $$32\text{m}^{2}$$ 