$18\mathrm{.}28$ The following data define the sea$-$level concentration of dissolved oxygen for fresh water as a function of temperature:

Estimate $\backslash ($ o $\backslash )(27)$ using $($a$)$ linear interpolation, $($b$)$ Newton's interpolating polynomial, and $($c$)$ cubic splines. Note that the exact result is $\backslash (7\mathrm{.}986\backslash$mathrm$\{$mg$\}/\backslash$mathrm$\{$L$\}\backslash ).$