The complete book of knitting/Abbey Barbara

Bought this book on eBay I love all the patterns but it does not tell me how many stitches to cast plus I’m not sure what multiple of 10sts plus 6 I’m confuse

Sounds like you can cast on any number of sts as long as you meet the multiple given for the pattern. A multiple of 10sts plus 6 means any number mulitplied by 10 e.g. 6x10, 8x10, 20x10. Then add 6 to that number. For the examples 60+6, 80+6, 200+6. The cast on would be 66, 86 or 206.