Mariam had ＄$$4y$$. After buying some cloth at ＄$$7$$ per metre, she had ＄$$y$$ left. How many metres of cloth did she buy? 
Overseas Competition->Knowledge Point->Word Problem Modules->Unitary Method Problems->Unitary Method with One Variable
Amount of money she spent to buy the cloth  $$\rightarrow$$＄$$4y-$$＄$$y$$  $$=$$＄$$3y$$,  Length of cloth she bought  $$\rightarrow$$＄$$3y\div $$＄$$7/\text{m}$$  $$= \frac{3y}{7}\text{m}$$. 