For the rectangle, the length was increased by 35%, and the width was decreased by 14%.

For the rectangle, the length was increased by 35%, and the width was decreased by 14%. By what percentage has the area of the rectangle changed?

The area of the rectangle was S = a * b, where S is the area, a is the length, b is the width
The length was a. After an increase of 35%, the new length is 1.35a:
a + (a * 35%) / 100% = a + 0.35a = 1.35a

The width was equal to b. After decreasing by 14%, the new width is 0.86b:
b – (b * 14%) / 100% = b – 0.14b = 0.86b

Then the new area of the rectangle is:
Snov = 1.35a * 0.86b = 1.161 * a * b = 1.161 * S

It turns out that the area of the rectangle was 100%, and became 116.1% (since 1.161 * 100% = 116.1%)

This means that the area of the rectangle has increased by 16.1%.
116.1% – 100% = 16.1%

Answer. Increased by 16.1%