To solve this expression, we need to follow the order of operations, which is parentheses, exponents, multiplication/division (from left to right), and addition/subtraction (from left to right).

First, let's simplify the expression inside the parentheses:
12 - 8 = 4

Now, let's square the result:
4² = 16

Next, let's divide the squared result by 8.2:
16 : 8.2 = 1.951219512195122

Finally, let's add 58 to the division result:
58 + 1.951219512195122 = 59.95121951219512

Therefore, 58 + (12-8) ² : 8.2 equals approximately 59.951.