A)
(-3/4 + 2/3) (-3/4 - 2/3)
= (-12/12 + 8/12) (-9/12 - 8/12)
= (-4/12) * (-17/12)
= 68/144
= 17/36

Б)
-3/4 + 2/3 (-3/4 - 2/3)
= -3/4 + 2/3 (-12/12 - 8/12)
= -3/4 + 2/3 * (-20/12)
= -3/4 + (-40/36)
= -9/12 - 40/36
= (-27/36) - 40/36
= -67/36