A minute has 60 seconds and Marcus is able to type 40 words per 30 seconds.
In a minute(60 seconds), Marcus can type 80 words. If you add another 30 seconds(one and a half minutes), Marcus can type 120 words per minute. Rhys is able to type 100 words in one and a half minutes which is less than Marcus' speed which is 120 words per one and a half minutes.