I think the answer to this problem is A
Answer:
A. 
Step-by-step explanation:
Given:
The regular polygon is a decagon having 10 sides.
Perimeter of the given polygon is,
.
We know that, perimeter of a regular polygon of
sides is given as,
where,
is the length of each side.
Here, 
Plug in these values and solve for
. This gives,

Therefore, the side length of the given polygon is 
17 meters because 5^2+12^2=17 meaning the answer must be d
SOLUTION:
To begin with, let's establish the problem as the following:
5 + 7
An effective method to solve this problem would be to convert it into a visual representation in order to obtain a better understanding.
As attached in the diagram above, I have demonstrated the problem visually. The five red circles / dots represent the five in the problem whilst the 7 circles / dots represent the 7 in the problem. Now we must simply count each of the circles / dots to obtain the total number which would be our final answer.
We can also simply use our fingers on our hands to solve the problem by counting 5 on our fingers and then adding 7 or vice versa to obtain the final answer.
FINAL ANSWER:
Hence, through either of these two methods, we obtain the final answer to the problem as follows:
5 + 7 = 12
Hope this helps! :)
Have a lovely day! <3