[(upper legth + lower length) x height] divided by 2
Well, i would use the distance formula to find the distance between the two points. Only issue- you do not have the other point, so lets find it!
We have the point 4,6. 4 is the x, and 6 is the y.
Lets start with 4 since the x works with the left and right aspect of the location. It says M has been translated 8 units to the left, meaning we go back 8. So if we are at 4, and we go back (A.K.A. Subtract) 8, we will be at -4.
Now lets move onto the y, which works with the up and down aspect of the location. It says M has been translated 9 unites down, meaning the point will be heading down and getting smaller. So if we are at 6, and we go down (A.K.A. subtract) 9, then we will be at -3.
So now we have the coordinates of point M (4,6) and point M' (-4,-3) so we can now complete the distance formula!
The distance formula helps determine the distance between two points. It looks like this: D = √(x₂-x₁)²+(y₂-y₁)²
Though it does not matter which order you use the coordinates in, i am choosing to use M and then M'.
So, starting with the X, X₂ will be -4 and X₁ will be 4.
Again, starting with the Y, Y₂ will be -3 and Y₁ will be 6.
So, the formula plugged in will look like this: d = √(-4 - 4)² + (-3 - 6)²
Solving it out, we first need to work within the parenthesis. Can you solve it?
Our outcome will be this: -8² + -9². But, since we are squaring (And a negative times a negative equals a positive) you can just write 8² + 9²
8²= 64
9²= 81
64+81 = 145.
So, the distance between point M and point M' would be 145 units
Hope this helps!
If it does not, please let me know so i can try to help!
Plug in the to X value in
If the series is made up of numbers in an arithmetic progression, you have

where

is the first term and

is the common difference between terms.
Since the last term in the series is

, you have

Solve the system

and you'll find that the first term is

(with

).