Probability problem long one

hey, guys, i have a really hard time with this, please help me

Suppose that the __probability__ that an individual has been exposed to high levels of carbon monoxide in their lifetime is __0.06__ and that the __probability__ that they have been exposed to high levels of nitrogen dioxide is __0.03__. What is the __probability__ that an individual has been exposed to __either__ high levels of carbon monoxide __or__ high levels of nitrogen dioxide but __not both__?

All i know is that i have to add them because they asked for "or" then i have to subtract because it is a "not both" problem but i have no idea what to subtract

Thank you for your help guys