If a surface has $75\%$ coverage of adsorption sites when the pressure of adsorbing gas is $6\mathrm{.}0$ atm, what will be the coverage when the pressure is $2\mathrm{.}0$ atm, assuming the adsorption is non$-$dissociative and follows the Langmuir adsorption isotherm?b$)$ For the same gas, what pressure is required to have only $1\mathrm{.}0\%$ surface coverage?