Why do I get N/A when I run linear aggression on excel?

Use Excel to identify a nonlinear (or curvilinear) trendline option with equation (put in yellow area) that may be a better fit,

Calculate/estimate the forecasted overhead expenses % for 2021 (year 8) for these three options.

Use a few sentences to describe the option you would select to estimate 2021 (year 8) overhead expenses along with rationale.