A plate on square base made of brass is of length x cm and width 1 mm. The plate weights 4725 gm. If 1 cubic cm cm of brass weight 8.4 grams, then the value of x is :

Answer: Option A

Given length and width of a square base plate of brass is x cm and 1 mm
Volume of the plate of square base = Area of base × height
$$\begin{array}{rl}& =x^2\times \frac{1}{10}\\ & =\frac{x^2}{10}cu.cm.\end{array}$$
According to the question,
$$\begin{array}{rl}& \Rightarrow \frac{x^2}{10}\times 8.4=4725\\ & \Rightarrow x^2=\frac{4725\times 10}{8.4}\\ & \Rightarrow x^2=5625\\ & \Rightarrow x=\sqrt{5625}=75cm\end{array}$$