Answer: Option D
Let original length = x and original breadth = y
Then,
Original area = xy
New area :
$$\eqalign{
& = \left[ {\frac{{\left( {100 - r} \right)}}{{100}} \times x} \right]\left[ {\frac{{\left( {105 + r} \right)}}{{100}} \times y} \right] \cr
& = \left[ {\left( {\frac{{10500 - 5r - {r^2}}}{{10000}}} \right)xy} \right] \cr
& \therefore \left( {\frac{{10500 - 5r - {r^2}}}{{10000}}} \right)xy = xy \cr
& \Rightarrow {r^2} + 5r - 500 = 0 \cr
& \Rightarrow \left( {r + 25} \right)\left( {r - 20} \right) = 0 \cr
& \Rightarrow r = 20 \cr} $$