1) 1 3/4 + (-1/2)
= 7/4 - 1/2
= 7/4 - 2/4
= 5/4
= 1 1/4

2) 4 3/8 + (-1/4)
= 35/8 - 1/4
= 35/8 - 2/8
= 33/8
= 4 1/8

3) 4 1/3 + (-7 5/9)
= 13/3 - 68/9
= 39/9 - 68/9
= -29/9
= -3 2/9