100 points:

What is 15 + 70?

An advertising firm has an old computer that can prepare a whole mailing in 6 hours. with the of newer model the job is complete in 2 hours. how long would it take the newer model to do the job alone?

Use set buikder notation to represent the following set: {, -2, -1, 0}

Find the area of the regular hexagon if a side is 20 cm.