Answer:
[tex]16\:\mathrm{ft^2}[/tex]
Step-by-step explanation:
Trish's initial garden had an area of [tex]8\cdot8=64\:\mathrm{ft^2}[/tex]. After expanding her garden to be 10 feet by 8 feet, the garden has an area of [tex]8\cdot 10=80 \:\mathrm{ft^2}[/tex]. Therefore, the garden was expanded by [tex]80-64=\boxed{16\:\mathrm{ft^2}}[/tex]