Answer:
look at the picture I have sent
For this case we have that by definition, the perimeter of a circle is given by:

Where:
r: It is the radius of the circle.
According to the figure, it is observed that the radius of the circle is 2. Then:

Let's remember that we have a quarter circle:

We round and we have that the correct option is 
Answer:
Option A
The attached figure is the image that completes the question
Answer:
7.4
Step-by-step explanation:
Answer:
The frequency of the burst of electromagnetic radiation which equals 1 exahertz = 10¹⁸ hertz.
Step-by-step explanation:
Since the frequency of the burst of electromagnetic radiation is 1 exahertz, and 1 exahertz = 10¹² megahertz. So, the frequency of radiation is 10¹² megahertz. Also 1 megahertz = 10⁶ hertz. So, 10¹² megahertz = 10¹² × 1 megahertz = 10¹² × 10⁶ hertz = 10¹² ⁺ ⁶ hertz = 10¹⁸ hertz.
So the frequency of the burst of electromagnetic radiation which equals 1 exahertz = 10¹⁸ hertz.
The awnsor is b hope this helped