a) 1,4 = 14/10 = 7/5
-28/5 + 7/5 = -21/5
b) 1 1/6 = (1*6+1)/6 = 7/6
7/6 * (-3/14) = -1/2*2 = -1/4
c) -16/27 : 4/9 = -16/27 * 9/4 = -4/3
d) -16,72 = -1672/100
-7,28 = -728/100
7/24 * (-1672/100) + 7/24 * (-728/100) = 7/24(-1672/100 -728/1000 = 7/24(-2400/100) = 7/24 * -24 = -7
