Does the X in math really represent that it value is still unknown?

Yes, but the X is only one of many variables that can be used to represent an unknown value. You can use any letter. though X is the most common.

no, b does not equal 5 in that equation

Step-by-step explanation:

if you solve for x, this is how it would look:

65/b + 8 x 4 = 20

65/b + 32 = 20

65/b = 20 - 32

65/b = -12

65 = -12b

-12b = 65

b = -65/12 (or -5 5/12)