You need to have two ways the variables are related. Take a look at some of the coin problems, mixture problems, tickets sold problems, etc. Do a search in the box at the top right and I'm sure you will see how they are done.
For example, if you have 7 coins (dimes and quarters) which add up to $1.15, then
d+q = 7
10d+25q = 115
How do you write a system of linear equations in two variables? Explain this in words and by using mathematical notation in an equation.
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