A shop sells bananas and pears.  Max bought $1$ banana and $3$ pears. He paid $84$p.  Emily bought $1$ banana and $1$ pear. She paid $48$p.  How much does $1$ banana cost? 
Overseas Competition->Knowledge Point->Word Problem Modules->Equation Word Problems->Multivariate Linear Equation Word Problems->Solving Problems by Solving System of 
Binary Linear Equations with Integer Coefficients 