What does the bar in set notation represent ?

Just add 10+3m the m means the roman numeral m is often used to indicate one thousand, and mm is used to indicate one million. for example, an expense of $60,000 might appear as $60m. sales of $3,000,000 might be written as $3mm. internet advertisers are familiar with cpm which is the cost per thousand impressions. so 10+3m= 300,000,010hope this and if it does can i have brainlest? if not tell me what i did wrong but i’m pretty sure i am right.