Respuesta :
Find the LCD between a/4 and a/3, which is 12, then turn a/4 into 3a/12 and a/3 into 4a/12 and then solve
(3a+4a) / 12 = 21 , 7a / 12 = 21, 7a = 12 x 21 = 252
a = 252/7 = 36 :)
(3a+4a) / 12 = 21 , 7a / 12 = 21, 7a = 12 x 21 = 252
a = 252/7 = 36 :)