Answer:
$273
Step-by-step explanation:
The grass area is smaller in both dimensions by 4 feet than the overall area. So the grass area is ...
26 ft by 21 ft = 546 ft^2
Since the installation cost is $0.50 per square foot, that cost is ...
($0.50/ft^2)(546 ft^2) = $273
$273 would be saved by not paying for installation.