The area of the rectangle is 80 m2, and its width is 5 dm. How much should the length

The area of the rectangle is 80 m2, and its width is 5 dm. How much should the length of the rectangle be reduced to reduce its area by 35 dm2.

Let’s write down the rectangle formula in general form and use it to solve this problem.
S = a * b.
Probably, there is a typo in the condition and the area is 80 dm². By condition, the area and width are known, we find the length of the rectangle:
a1 = S1 / b1 = 80/5 = 16 (dm).
The area of the new rectangle is:
S2 = S1 – 35 = 80 – 35 = 45 (dm²).
The width remains unchanged: b2 = b1 = 5 dm.
Find the length of the new rectangle:
a2 = S2 / b2 = 45/5 = 9 (dm).
a1 – a2 = 16 – 9 = 7 (dm).
Answer: the original length must be reduced by 7 dm.