A group of students is arranging squares into layers to create a project. The first layer has 6 squares. The second layer has 12 squares. Which formula represents an arithmetic explicit formula to determine the number of squares in each layer? f(1) = 6; f(n) = 6 + d(n − 1), n > 0 f(1) = 6; f(n) = 6 ⋅ d(n − 1), n > 0 f(1) = 6; f(n) = 6 ⋅ d(n + 1), n > 0 f(1) = 6; f(n) = 6 + d(n + 1), n > 0