A wall, initially having dimensions of 3.00m by 12m, with a transmission loss of 25db, has a glass window added. The window, 1.00m by 2.00m, contributes a transmission loss of 5db. What is the total transmission loss for the wall with the window installed? 
a) 30db 
b) 20db 
c) 25db 
d) 15db