Six pears and three apples cost $3.90. Two pears and five apples cost $3.30. How much does one pear cost?
Let's first translate that in "the language".
We multiply the second equation (all of it) by 3, because that will also give us the price of 6 pears plus apples (as in the first), and the price difference will only be caused by the different number of apples:
Put this into one of the equations: