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?

a1 = 6; an = 6 + an − 1, n > 0

a1 = 6; an = 6 ⋅ an − 1, n > 0

a1 = 6; an = 6 ⋅ an + 1, n > 0

a1 = 6; an = 6 + an + 1, n > 0