20b-16 isn't an equation so it can't be solved, but there's a common factor 4 which simplifies the expression to 4(5b-4). Another thing you can do with this is to plot it on a graph: let y=20b-16, and when you plot it you will get a straight line passing through -16 on the y axis (vertical) and 4/5 or 0.8 on the b axis (horizontal), so it's a line with a very steep slope (/). The graph helps you to see the expression.