To find the area of the rectangular mural, we first need to determine the length of both sides.
The shorter side measures 5 yards. The longer side is 3 yards longer than the shorter side:
\[ \text{Longer side} = \text{Shorter side} + 3 \text{ yards} = 5 \text{ yards} + 3 \text{ yards} = 8 \text{ yards} \]
Now we can calculate the area \( A \) of the rectangle using the formula:
\[ A = \text{length} \times \text{width} \]
Substituting the values we have:
\[ A = 5 \text{ yards} \times 8 \text{ yards} = 40 \text{ square yards} \]
Thus, the area of the mural is \(\boxed{40}\) square yards.