Question 1065556
The ceiling and four walls:
{{{(18.5)(14.25)+2*(18.5)(8)+2*(14.25)(8)}}}
{{{263.625+16*18.5+16*14.25}}}
{{{263.625+524}}}
{{{787.625}}}, square feet



Cans of paint?
{{{787.625*sqft*(1/275)(gallons/sqft)}}}

about 2.86 gallons;
Rounding to the nearest whole gallon, 3 gallons to purchase.


ANSWER:  3 gallons