Answer: 12.32%
Explanation:
1.
is the original long side and
is the original short side.
2. The area of the original rectangle is
.
3. The rectangle is extended 4% on the long sides and 8% on the short sides. therefore, the new long side is:

4. And the new short side is:

5. The new area is:

6. The percentage of increase is calculated by substracting the new area and the original area:

7. The result is:
(0.1232)(100)=12.32%