The Brunauer-Emmett-Teller BET theory is a widely used method for calculating the surface area of solid adsorbent materials. The BET equation is given by:N = N_m * C * P / [ 1 - P * 1 + C - 1 * P ]where N is the amount of gas adsorbed at a given pressure P, N_m is the amount of gas adsorbed in a monolayer, and C is the BET constant.First, we need to find the amount of gas adsorbed in a monolayer N_m . We are given that the number of monolayers formed is 4. Therefore, the total amount of gas adsorbed N_total can be calculated as:N_total = N_m * 4Now, we can use the BET equation to find N_m:N_m = N_total * 1 - P * 1 + C - 1 * P / C * P We are given the value of the BET constant C = 0.05 . However, we do not have the value of the pressure P. In order to solve this problem, we need more information about the adsorption isotherm, such as the pressure at which the adsorption occurs or the relationship between the amount of gas adsorbed and the pressure.Assuming we have the value of N_m, we can then calculate the surface area of the solid adsorbent material using the following equation:Surface area = N_m * area occupied by each adsorbed layer * Avogadro's number / mass of the adsorbent materialwhere Avogadro's number is 6.022 x 10^23 molecules/mol.Once we have the value of N_m, we can plug it into this equation along with the given values to find the surface area of the solid adsorbent material.