Over which interval does h have a negative average rate of change

Add the two expressions 3.8b - 7 and 2.9b + 9 enter your answer in simplified form

Aschool puts on a play. the play costs $1,200 in expenses. the students charge $4.00 for tickets. there will be one performance of the play in an auditorium that seats 500 people. what is the domain of the function that shows the profit as a function of the number of tickets sold?  

Twelve less than a number is at most 20