For this case, we propose a rule of three, since with \ frac {2} {3} of gallons it covers 3% of wall, then:
gallon --------> 3%
1 gallon -----------------------> x
Where the variable "x" represents what percentage of wall can be painted with 1 gallon of paint. So:
Thus, with 1 gallon of paint 4.5% of wall are painted.
Answer:
4.5%