a) (-1)/6 + 0,75 = -1/6 + 3/4 = (-1/6) * (2/2) + (3/4) * (3/3) = -2/12 + 9/12 = 7/12

b) 31/10 - 3/8 = (31/10) * (4/4) - (3/8) * (5/5) = 124/40 - 15/40 = 109/40

c) 0,1 + (-9)/17 - (-99) = 0,1 - 9/17 + 99 = (0,1 * 17/17) - (9/17) + 99 = 1.7/17 - 9/17 + 99 = (1.7 - 9 + 99)/17 = 91.7/17

d) 5,75 + (-8)/9 = 5.75 + (-8/9) = 5.75 * (9/9) + (-8/9) = 51.75/9 + (-8/9) = (51.75 - 8)/9 = 43.75/9

e) 19/8 × (-0,4) = (19/8) * (-0.4) = -7.6/8 = -19/20

f) (-12)/5 ÷ (-6,5) = (-12/5) / (-6.5) = (-12/5) * (-1/6.5) = 12/5 * 1/6.5 = 12/32.5

g) 0,2 + 2,5 ÷ 7/2 = 0.2 + (2.5 * 2/7) = 0.2 + 5/7 = (0.2 * 7/7) + 5/7 = 1.4/7 + 5/7 = 6.4/7

h) (0,25 - 5/6) × 1,6 + 1/3 = (0.25 * 6/6 - 5/6) * 1.6 + 1/3 = (1.5/6 - 5/6) * 1.6 + 1/3 = (-3.5/6) * 1.6 + 1/3 = -5.6/6 + 1/3

i) 1/9 - 0,3 × 5/9 + 1/3 = 1/9 - (0.3 * 5/9) + 1/3 = 1/9 - 1.5/9 + 1/3 = (1 - 1.5 + 3)/9

h) (4/5 - 1) ÷ 3/5 - 2/3 × 0,5 = (4/5 - 1) / (3/5) - (2/3) * 0.5 = (4/5 - 1) / (3/5) - 1/3 = (4/5 - 1) * (5/3) - 1/3 = (4 - 5*1) * (5/3) - 1/3 = (-1) * (5/3) - 1/3 = -5/3 - 1/3 = -6/3 = -2