In order to get the average of a list on numbers, we have to take the sum of all the numbers and divide them to how many they are.
Making that statement an equation, we do:
Notice that we divide it by 5 because we have 5 numbers. We equate it by x because the problem says that it should be the average.
Divide both sides by 5,
Combine all the constants,
Therefore, we get 26 as x.
In order to check if we got the right answer, substitute 26 on x and see if you get an equation.
Hope that helps.