Robert has x books. Marie has twice as many books as Robert has. Together they have 18 books. Which of the following equations can be used to find the number of books that Robert has?

❤️ (geometry) does the construction demonstrate how to copy an angle correctly using technology a) yes; the distance between points a and f was used to create circle h b) yes; the distance between points f and g was used to create circle h c)no; the distance between points a and f was used to create circle h d) no; the distance between points f and g was used to create circle h