`\text{a)}` `(-27) . 94 = -2538 ; (-93) . (-61) = 5673`
`\text{b)}` `3/5 - (-1/15) = 9/15 + 1/15 = 10/15 = 2/3` `;`
`-5/4 + 3/4 = (-5 + 3)/4 = -2/4 = -1/2`
`\text{c)}` `-1/7 + (3/5 + 3/21) = (-1/7 + 3/21) + 3/5 = 0 + 3/5 = 3/5`
`\text{d)}` `(3/4 - 16/12) + (1/3 - 27/36) + 5/96 = (3/4 - 27/36) + (1/3 - 16/12)`
`= (27/36 - 27/36) + (4/12 - 16/12) = 0 + (-12)/12= -1`