The line graph shows the cost of inflation in some country. What cost $$100$ in $1999$ would cost the amount shown by the graph in subsequent years. Below are two mathematical models for the data shown in the graph. In each formula, C represents the cost x years after $2010$ of what cost $$100$ in $1999.$ Answer parts $($a$)$ through $($c$).$

Model $1C=1\mathrm{.}9x+125\mathrm{.}4$

Model $2C=0\mathrm{.}02x^2+1\mathrm{.}8x+125\mathrm{.}6$

a$.$ Use the graph to estimate the cost in $2018$ of what cost $$100$ in $1999.$

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