ANSWER
The smaller number is 7.
EXPLANATION
Let the numbers be x and y.
Then we have;
y-3x=3... eqn (1)
If the sum of the numbers is 3 then,
y+x=31... eqn (2)
Eqn(2) - Eqn (1)
x--3x=31-3
Divide both sides by 4,
We put x=7 into the second equation,
y+7=31
y=31-7
y=24
The smaller of the two numbers is 7.