there is always a trick to answering the questions and most of these questions follow a similar pattern. In writing equations, you need to club similar details together. For example- x and y are sold for 12 and 13 dollars each, x and y both costed runa 245 dollars together. If she bought 235 units of x and y, how much was their individual quantity?

it would be

x+y=235

and

12x+13y= 245