The area of the garden of design A is:
[tex]A_A=\lparen9)\left(12\right)=108[/tex]The area of the garden of design B is:
[tex]A_B=\pi\left(5\right)^2=78.54[/tex]To determine the cost for each design we multiply the cost per square ft by the area of each garde.
For design A we have:
[tex]\left(4.20\right)\left(108)\right?=453.60[/tex]For design B we have:
[tex]\lparen4.20)\left(78.54\right)=329.87[/tex]Therefore, design A cost $453.60 and design B cost $329.87