how many gallons of paint are needed for one coat on the entire exterior of the barn, including roof?

Answer:
23
Step-by-step explanation:
21·21=441÷2·2=441
24·60=1,440·2=2880
24·40=960·2=1,920
441+2880+1920=5,241
5,241÷400=13.1025 which is goes upto 23