The series 7 + 16 + 25 +34 +43 +52 + 61 is an illusration of arithmetic series
The sigma notation of the series is: 
<h3>How to write the series in sigma notation?</h3>
The series is given as:
7 + 16 + 25 +34 +43 +52 + 61
The above series is an arithmetic series, with the following parameters
- First term, a = 7
- Common difference, d = 9
- Number of terms, n = 7
Start by calculating the nth term using:
a(n) = a + (n - 1) * d
This gives
a(n) = 7 + (n - 1) * 9
Evaluate the product
a(n) = 7 - 9 + 9n
Evaluate the difference
a(n) = 9n - 2
So, the sigma notation is:

Read more about arithmetic series at:
brainly.com/question/6561461
The answer is 14
..........
Answer:
The numbers are 9, 19 and 76.
Step-by-step explanation:
Let's take the second number and make it a variable, like x. Now let's find all the other numbers in terms of x.
The first number in terms of x:

The second number in terms of x:

If we add them all up, these 3 numbers in terms of x must be equal to 104, so:

Now that we know the second number, we can find the other numbers since we already figured out their values in terms of x:


The first number is 9, second number 19 and the third number 76.
If the height is 6ft then the base is 13ft.
78/6=13
Hope this helps.