i have a question on post optimality analysis reguarding a simplex tableau

a company makes desks, types 1, 2, 3, and 4, with some constraints on machine hours per week and materials availiable. i have maximized the profit.
i have optimized the tableau using the simplex algorithm, and so have the finished table in front of me. i am then told that 100 desks of type 2 must be included in the optimum result. how do i find the new optimal production without starting from scratch again? its kinda urgent so any help i'd appreciate. cheers.