Jack and Serena can write a lab report together in $6$ hours. If all people work at the same rate, how many hours would it take to write a lab report if Kay joins Jack and Serena?

  4 hours

Step-by-step explanation:

If all work at the same rate, the time required is inversely proportional to the number of people on task. If the number of writers goes from 2 to 3 (is multiplied by 3/2), the time required will be 2/3 of that for 2 people:

  (2/3)(6 hours) = 4 hours

If Kay joins Jack and Serena, the lab report can be done in 4 hours.

the final price would be 29.6925

step-by-step explanation:

39.59 minus 25% equals 29.6925

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.