Mark builds an apartment that is 16 by 10 feet.  There are 6 rooms in total.  All the rooms are the same size except the living room which is as big as 3 other rooms.  How big is the living room?
Total square footage is 16*10=<<16*10=160>>160 square feet

There are 3+3=<<3+3=6>>6 rooms
6-1=<<6-1=5>>5 of them are the same size
If x is the size of the normal room then the square footage of all rooms is 5x+3x=8x
So each room is 160/8=<<160/8=20>>20 square feet
So the living room is 20*3=<<20*3=60>>60 square feet
#### 60