what would be the equation for: Jim has $30 gift certificate for a movie. Each time Jim sees a movie, m, $5, is deducted from the gift card balance, b. whats

what would be the equation for: Jim has $30 gift certificate for a movie. Each time Jim sees a movie, m, $5, is deducted from the gift card balance, b. whats the equation describing b in terms of m

 

Thanks in advance