Let's denote the length of the back wall as \( L \) (which is given as 3.25 feet) and the width of each of the two sides as \( W \).
According to the problem, the total length of all three sides is 6 feet. This gives us the equation:
\[ L + 2W = 6 \]
Substituting the value of \( L \) into the equation:
\[ 3.25 + 2W = 6 \]
Now, we can solve for \( W \):
- Subtract 3.25 from both sides:
\[ 2W = 6 - 3.25 \]
\[ 2W = 2.75 \]
- Divide both sides by 2:
\[ W = \frac{2.75}{2} \] \[ W = 1.375 \]
Thus, the length of each side (width) of the shelter is \( 1.375 \) feet.