Dear Mr. Sam,
I am writing this letter to let you know that, I would not be able to take over the receptionist work during her lunchtime. I have got a project delivery by tomorrow and many tasks are pending, which need to be submitted by today evening.
If I explain myself, as per the project schedule we should be delivering it last week, however, as there were some technical issues which have delayed us giving on time. I had to request the client to give us some extra time so, that we can give a quality product. As you always know that I had never let down any of our customers and want to continue the same. Moreover, I am not good at customer executive service and I do not think that I am qualified to handle the receptionist work.
I would recommend that we can ask someone from the sales team to take up this work temporarily they will be perfect for this work. Once again, I would like to apologize for not helping out.
Yours Sincerely,
Ross. 
Dear Mr. Sam,
I am writing this letter to  
let
 you know that, I would not be able to take over the receptionist work during her lunchtime. I have  
got
 a project delivery by tomorrow and  
many
 tasks are pending, which need to  
be submitted
 by  
today evening
.
If I  
explain
 myself, as per the project schedule we should be delivering it last week,  
however
, as there were  
some
 technical issues which have delayed us giving on time. I had to request the client to give us  
some
 extra time  
so
, that we can give a quality product. As you always know that I had never  
let
 down any of our customers and want to continue the same.  
Moreover
, I am not  
good
 at customer executive service and I do not  
think
 that I  
am qualified
 to handle the receptionist work.
I would recommend that we can ask someone from the sales team to take up this work  
temporarily
 they will be perfect for this work. Once again, I would like to apologize for not helping out.
Yours  
Sincerely
,
Ross.