The surface area of a cube is 600 square inches. What is the area of one of its faces?

Area of a square = side^2

area of a cube = 6 x side^2

let the side be a.

6a^2 = 600

=> a^2 = 600/6

=> a^2 = 100

Hence the area of one of its faces is 100 square inches.

or in plain terms without using those formulas,

6 faces of the cube have 600 square inches

=> 1 face of the cube has 600/6 = 100 square inches