I am not sure I can see all of the grey squares. To do this simply count the grey squares in the box and the number of white squares and write them as a ratio in grey:white format. When treated as a fraction (all ratios are fractions no matter what format they are written) the ratio can be reduced.
a. 3:3 or 1:1 when reduced
b. 8:1
c 3:6 or 1:2 when reduced
d. 7:8
e. 24:40 or 3:5 when reduced