Based on the calculations, the unknown number is equal to 
- Let the unknown number be x.
<h3>How to find an
unknown number:</h3>
Translate the word problem into an algebraic expression, we have;
Adding 21 to the unknown number:

Multiplying the result by 3:

84 more than two-thirds of the unknown number:

Equating the equations, we have:

Cross-multiplying, we have:

Read more on word problems here: brainly.com/question/13170908
Answer:
, domain: all real numbers
Step-by-step explanation:
The two functions that we have in this problem are:

and

Here we have to calculate
(f+g)(x)
Which is equivalent to:

Taking the two functions and substituting into this expression, we find:

We also have to find the domain of the new function. However, we notice that there are no restrictions on the value of x, since this is a second-order function with no denominators, logarithms or roots: therefore, the domain is all real numbers.
Why did you delete my question? but the answer maybe 24 if you divide by 48