Solve the system of equation of 2x+6y=-1 and 6x-21y=10?

Jeffery conducted a survey in his school and found that 30 of the 50 eighth grade students' favorite subject is mathematics. based on the results, jeffery concluded that out of the 200 students in his school, 120 students' favorite subject is mathematics. select the statement that is true about jeffery's conclusion. a. jeffery's conclusion is not valid because the sample was biased since only 200 students were surveyed. b. jeffery's conclusion is valid because the sample was random since all of the students were eighth grade students. c. jeffery's conclusion is valid because the sample was random. d. jeffery's conclusion is not valid because the sample was biased since all of the students were eighth grade students.

If 10 men take 18 days to mow 60 acres of grass, how long will 15 men take to mow 80 acres?

Suppose a gym membership has an initial enrollment fee of $75 and then a fee of $29 a month. which equation models the cost, c, of the gym membership for m months?