The independent variable is the variable you change.
The dependent variable is the variable you measure that depends on the independent variable.
Since b is the independent variable, you need to isolate/get the variable "a" by itself in the equation: [this is because "b" is the variable you change, and "a" is the variable you measure that results/depends on "b"]
4a + b = -52 Subtract b on both sides
4a + b - b = -52 - b
4a = -52 - b Divide 4 on both sides to get "a" by itself

