Since a total of 55 people rated it good/very good, we know that 1/3 of the viewers are 55 people. So we can set the equation: 1/3x=55
Now, just multiply both sides by 3 (or divide by 1/3, same thing) and get your answer!
The equation (form) is: 
The solution of the equation is: 
Explanation:
First, let's call the number we are going to solve for "x".
Then two thirds of this number can be written as:

Then "plus 4" means add 4 we get:

"is 7" means that the above expression is equal to 7 (as follows):

The solution of the above equation is:
