How do you write the mathematical expression for “8 more than a number x”?

Hint: In order to find the mathematical expression consider the “more than” phrase as addition $ ' + ' $ symbol and write the expression in terms of x.

Complete step-by-step answer:
In order to write any mathematical expression from some words and figures ,we must first find the relationship and the quantities specified .
Here in this question the relation between 8 and x is that its saying that something is 8 more than than a some number x .So here more than means addition
So we are replacing the more than word from the sentence with the addition symbol
8 more than x
replacing more than with addition $ ' + ' $ symbol.
 $ = 8 + x $
And then a question arises who is 8 more than x ,so we don’t know who is ,so let it be y,
So , now our question has become perfect to say that
y is 8 more than a number x
replacing more than with addition $ ' + ' $ symbol.
 $ y = x + 8 $
So, the correct answer is “ $ y = x + 8 $ ”.

Note: 1.Mathematical equation : A Mathematical equation can be defined as the mathematical statement which contains an equal symbol $ = $ in between two algebraic expressions that share the same value .
A algebraic expression can contain any number of variables generally we take 2-3 variables
Let assume a expression
 $ 5x + 9 = 24 $
It is a mathematical equation having LHS (Left-Hand-Side) equal to RHS (Right-Hand-Side)
Where $ x $ is the variable
5 is the coefficient of variable $ x $
And $ 24,9 $ are the constants
2. $ 2x + 98 + 78y $ is not a mathematical equation because it does not contain equality $ = $ symbol .
It is only a mathematical expression.
3. Read the statement carefully in order to convert them into mathematical expressions.