Question 419504
Certainly the notation is confusing, but a general "rule of thumb" is that a "unit of percent" is really a number divided by 100.  For example, 8%, when expressed as a number is really (8/100) = .08.

In your formula, then, if you substitute (x/100) for the expression x%, you can solve the equation:

x/100 = (2x + 1)/300
(300x)/100 = 2x + 1  (multiplying both sides by 300)
3x = 2x + 1  (simplifying the left side)
x = 1  (subtracting 2x from both sides)

So, x = 1.

Let's check the answer:
x% = (2x + 1)/300
1% = ((2 * 1) + 1)/300
1% = 3/300 = 1/100  which is true.