в) -4,2 - 3,25 - (-1/12)

1. Convert decimals to fractions: -4.2 = -42/10 = -21/5, -3.25 = -325/100 = -13/4.
2. Rewrite the expression: -21/5 - (-13/4) - (-1/12) = -21/5 + 13/4 + 1/12.
3. Find a common denominator (60) and add: (-252 + 195 + 5) / 60 = -52/60 = -13/15.