Theory:

Now we have to find out the values of algebraic expressions using the given variables.
Steps to find the value of the algebraic expression:
  
Step \(1\): Understand the problem first and then fix the variable and write the algebraic expression.
 
Step \(2\): Substitute each variable by the given numerical value to get an arithmetical expression.
 
Step \(3\): Try to solve or simplify the arithmetical expression by the BIDMAS method.
 
Step \(4\): Now, the final value you obtained is the required value of the expression.
Example:
Question I)

Consider the algebraic expression 13m9n8 and the value of \(m=\) 12 and \(n=\) 4.
 
Now substitute the values of \(m\) and \(n\), we get
 
=13(12)9(4)8=156368=15644=112
 
Therefore, the value of the algebraic expression 13m9n8 \(=\) 112.
  
Question II)

Consider the algebraic expression m24n2+4 with the value of \(m=\) 12 and \(n=\) 4.
 
Now substitute the values of \(m\) and \(n\), we get
 
=1224(42)+4=1444(16)+4=14464+4=14864=84
 
Therefore, the value of the algebraic expression m24n2+4 \(=\) 84.
 
Question III) 

Consider the algebraic expression is 2m28n2+13 with the value of \(m=\) 12 and \(n=\) 4.
 
Now substitute the values of \(m\) and \(n\), we get
 
=2(122)8(42)+13=2(144)8(16)+13=288128+13=301128=147
 
Therefore, the value of the algebraic expression 2m28n2+13 \(=\) 147.