Translate the following sentence into an equation using n for the unknown number. Then solve for n. when 15 is decreased by three times a number, the result is 21 a. 15 minus 3 n = 21. n = negative 2. b. 3 n minus 15 = 21. n = negative 2. c. 3 n minus 15 = 21. n = 12. d. 15 minus 3 n = 21. n = 2. Please select the best answer from the choices provided A B C D