Which problem can be solved using the expression 400+100c=550+70c?

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One car salesperson makes a monthly salary of $400, plus $100 commission for each car sold.  

The other car salesperson makes a monthly salary of $550, plus $70 commission for each car sold.

For which number of cars, c, do they make the same amount in one month?

c.

step-by-step explanation:

because first you have to add the 4x, 9x, and the 7x together and you get 20x and then you add the last numbers up and you get 5and then you put the subtraction sign in there and that's how you get the answer.