Need help with ratios quick plss

For the equation below, x is the input and y is the output. y = -4x + 3 if the input is -8, then the output is

Afruit stand has to decide what to charge for their produce. they need $10 for 4 apples and 4 oranges. they also need $15 for 6 apples and 6 oranges. we put this information into a system of linear equations. can we find a unique price for an apple and an orange?

How do you determine if an ordered pair is a solution to a given equation?