Theory:

Factorisation by taking out the common factor from each term
1. Consider the expression 3x315x2+12x.
 
In all the term, 3x is taken commonly outside.
 
3x×x2+(3x×5x)+(3x×4)
 
=3x(x25x+4)
 
 
2.  Consider the expression 10xy+5x3y.
 
Here the term 5xy is common in the expression.
 
10xy+5x3y
 
=5xy×2+5xy×x2=5xy2+x2