421 ÷ 35 × 299.97 ÷ 25.05 = ?²

$$\eqalign{ & {\text{Let the number be }}x \cr & {\text{Given }} \cr & 421 \div 35 \times 299.97 \div 25.05 = {x^2} \cr & \approx {\left( x \right)^2} = 420 \div 35 \times 300 \div 25 \cr & \approx 12 \times 300 \div 25 = 12 \times 12 \cr & \approx {x^2} = 12 \times 12 \cr & \therefore x = \sqrt {12 \times 12} = 12 \cr & {\text{Hence the number is 12}} \cr} $$