5.523 Найдите частное:

a) 4/9 : 4/16 = 4/9 * 16/4 = 16/9.
б) 2/7 : 2/9 = 2/7 * 9/2 = 9/7.
ж) 12/25 : 8/15 = 12/25 * 15/8 = (3*4)/(5*5) * (3*5)/(2*4) = 9/10.