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Which expressions are equivalent to -6 + 3m

Which is the equation of a line perpendicular to the line with the equation 3x+4y=8

Each month, a shopkeeper spends 5x + 14 dollars on rent and electricity. if he spends 3x−5 dollars on rent, how much does he spend on electricity? for which value(s) of x is the amount the shopkeeper spends on electricity less than $100? explain how you found the value(s).