For this case what we have to take into account is the following variable: x = represent the unknown number We now write the following inequality: "four times the sum of number and 15 is at least 20" 4 (x + 15)> = 20 We clear the value of x: (x + 15)> = 20/4 (x + 15)> = 5 x> = 5 - 15 x> = - 10 The solution set is: [-10, inf) Answer: all possible values for X are: [-10, inf)