Given that we assume that all the bases of the triangles are parallel.
We can use AAA or Angle-Angle-Angle to prove that these triangles are similar.
Each parallel line creates the same angle when intersecting with the same side.
For example:
The bases of each triangle cross the left side of all the triangle.
Each angle made by the intersecting of the the parallel base and the side are the same.
Thus, each corresponding angle of all the triangles are congruent.
If these angles are congruent, then we have similar triangles.
Answer:
mean= sum of the terms/ (over) number of terms
Expression simplified: 
Step-by-step explanation:
The expression that we have in this problem is:

The first type of operation that we have to solve in such expression are multiplication/division.
In this expression, there is only one multiplication, that is:

So we can rewrite the expression as

Now we can evaluate the sum of the similar terms: in this case, similar terms are only 3 and 4, and their sum is

Therefore, the expression can be rewritten as

Learn more about simplifying expressions:
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A median is the middle number of a data set.
To find it put the numbers in order.
78, 69, 69, 96, 99
Then find the middle number
78, 69, *69,* 96, 99
The median is 69
A mode is the number that appears the most in a set of numbers.
78, *69, 69,* 96, 99
The mode is 69
To find the mean or average of a set of numbers, add all the numbers together then divide by the number of numbers there are.
99+69+96+69+78 = 411
411/5 = 82.2
The mean is 82.2
Hope this helped! If you have anymore questions or don't understand, please comment on my profile or DM me. :)