I believe you would multiply 28 by 7, then add that to 460
You start with 100%, add 80% for the increase and you get 180%, take away 40% for the decrease and you get 140%
The diagram of the lawn and the shed is shown below.
The area of the lawn needed to be mowed equals to the area of the yard minus the area of the shed
The area of the yard =

The area of the shed =

The area of the lawn =

The area of the lawn =

The area of the lawn =