According to PEMDAS, the expression inside parentheses is evaluated first, so, evaluate (3) as 3, then continue.
Next, according to PEMDAS, 6^2 is evaluated, so replace that with 36.
Now, you have 36/2*3 + 4 and you have to decide whether to divide first or multiply first. This is the real problem.
Since MD are on the same precedence level and AS are on the same precedence level, the rule is to perform them in left-to-right order. This means the expression becomes 18*3 + 4, then 54 +4, then 58.
This is different from 36/(2*3) + 4, which is 36/6 + 4, which is 6 + 4 = 10.
Thus, (3) means that 3 is multiplied by what is next to it, but is that 2 or is that 6^2/2 ? Parentheses would clarify that, but, without parentheses, the left-to-right-rule prevails.