Question 1048480
From the first blueprint, the living room actual length is l, where l is:

{{{l = 4.5*4 ft = 18 ft}}}
Now at the second copy, the length of the (designed) living room must be L, where:

{{{L = (actual length l)/(scale of 2nd blueprint) = (18 ft)/(3 ft/inch) = 18/3 = 6 in}}}