Average growth rate = 4.2 cm/week.
So, common difference d = 4.2
The height of the tree a0 = 200 centimeters.
The height of the tree after end of the first week a₁ = 200 + 4.2 = 200 + 4.2(1)
The height of the tree after end of the second week a₂ = 200 + 4.2 + 4.2 = 200 + 4.2(2).
The height of the tree after end of the third week a3 = 200 + 4.2 + 4.2 + 4.2 = 200 + 4.2(3).
The height of the tree after the end of the nth week an = 200 + 4.2(n).
The equation is a_n = 200 + 4.2(n).
