what is the regular expressions in "R" that find all words that: Start with a letter1 and End with another letter2? : i'm trying to work out the exercise from a book called "R for data science" on regular expressions.

there's this question which i'm unable to solve :

1.Given the corpus of common words in stringr::words, create regular expressions that find all words that:

1.Start with “y”.  
2.End with “x”  
3.Have seven letters or more.

example :    
 
    sentence <- "i want to extract these - yandx,ynx and yrax,romanav "

    #it would be helpful to find how to do these with stringr::str_view() function.


also please suggest me some good resources to refer for learning regex in r .



