Question 615428
Multiply EVERY term by the LCD 1-s to go from


(s/(1-s))*e^B/(1+(s/(1-s))*e^B) 


to


(se^B)/(1-s+se^B)



Now you can factor out an 's' from the last two terms in the denominator to get what your book got


(se^B)/(1-(1-e^B)s)