Question 150180
You need to loook on the area of the room right? What is that 2.5metres from your measurement?...thickness?- which you don't need
The {{{Area}}}  of the bedroom is 4mx5m= {{{20m^2}}}
And the wallpaper roll can only cover an {{{Area}}} of {{{6m^2}}} ----> 6mx 1m
So, you need </pre><font size = 4 = "indigo"><b>4</pre> 
rolls to cover the room Area----> {{{4 x 6m^2}}} ---> {{{24m^2}}}. This is enough because the room is only {{{20m^2}}}

Thank you,
Jojo