the common difference can be found by subtracting the first term from the second term.....33 - 28 = 5....so the common difference (d) = 5
an = a1 + (n - 1) * d n = the term u want to find = 11 a1 = first term = 28 d = common difference = 5 now we sub a11 = 28 + (11 - 1) * 5 a11 = 28 + 10 * 5 a11 = 28 + 50 a11 = 78