When you write a function in the form
, y is the dependent variable, and x is the independent variable.
So, if b is the independent variable, it means that we have to solve the expression for r.
To do so, we perform the following steps: start with

Add 12 to both sides

Divide both sides by 4:

So, we wrote the expression in the form
, which means that r is the dependent variable and b is the independent variable, as requested.
Not sure what x' means but
seems to be the reverse distributive property
normally written as
a(b+c)=ab+ac
we can see the similarity
a(x'+y)=ax+ay
distributive property
First, start at zero. Now, because we are multiplying -4 by 3, we will jump over by 4 to the left ; 3 times on the number line. We should reach -12, and if we check our work, 3 x -4 = -12.
51, 53, 55, 57, 59. it's simple.
You would have to divide $2.50 by $14.30 and you will get your answer