The correct answer is (d) 840
Easy explanation: For wall, length = 3m = 300cm, breadth = 12cm and height = 7m = 700cm
Volume of the wall = 300 * 12 * 700
= 2520000cm^3
Volume of bricks = 25 * 12 * 10
= 3000cm^3
Number of bricks required = \(\frac{Volume \,of \,the \,wall}{Volume \,of \,one \,brick}\)
= 252000/3000
= 840.