21 - 16.75 is 4.25. Do the problem on a calculator and you'll get it.
The answer is B. Yes; 4
Arithmetic sequence is the type of sequence of numbers which difference between each number will always remain constant
in the sequence above we could see the difference between one number with another is exactly 4:
15 + 4 = 19
19 + 4 = 23
23 + 4 = 27
Answer: 
Step-by-step explanation:
For this exercise it is important to remember the multiplication of signs. Notice that:

In this case you have the following expression given in the exercise:

Then you can follow the steps shown below in order to solve it:
Step 1: You must solve the subtraction of the numbers 0,65 and 3,21. Then:

Step 2: Now you must find the product of the decimal numbers above. In order to do that you must multiply the numbers.
(As you can notice, both are negative, therefore you know that the product will be positive).
Then, you get that the result is the following:

True
11 is √121
12 is √144
So √131 is in between 11 and 12