Answer:
 all 4 ways of solving equations all have different rules you have to follow. 
 Multiply fractions / Dividing fractions: Sometimes when doing common factor, you need to multiply and divide fractions. 
 Adding fractions // Subtracting fractions: necessary because operations with fractions need algebraic sum to clear unknowns. 
 Simplifying fractions: To rewrite the results, it is necessary to simplify fractions