I am not sure if my method is correct, but here's how I think you should approach this problem:

Total number of people = 248
Number of married people = 156
Number of self employed people = 70
Number of people who are married AND self employed = 25% of 156 = 39
Number of people who are self employed but not married = People self employed - People self employed/married

Thus, number of people who are self employed but not married = 70-39 = 31

Thus probability = 31/248 = 1/8

Does this match the correct answer specified?

Also, I've attached a diagrammatic view of how this might work.

@Others: Please let me know if my approach is right!

Many thanks. You have got it right.

hi
both self employed and married
= 156 * (25/100) = 39

only self employed = 70 - 39 = 31
probability:

only self employed / total
= 31 / 248
= 1/8

thanks
cheers through the kudos button if this helps