Answer
5 cats have green eyes without stripes
Work Step by Step
# of striped w/out green eyes + # striped w/green eyes = 10
# striped w/green eyes = 7
# of striped w/out green eyes + 7 = 10
# of striped w/out green eyes + 7 = 10
# of striped w/out green eyes + 7 -7 = 10 -7
# of striped w/out green eyes =3
total cats - # striped w/out green eyes = # green eyes w/out stripes
15 - 3 - 5 = 5