Johnny drove 300 miles to meet his mother on Tuesday. On Thursday, he drove 120 miles to meet friends at an amusement park. On Saturday, he drove 420 miles back home. The entire trip took 14 hours. What was his average driving speed?

The area of a rectangle is 10 cm^2. one side of the rectangle is x cm. express the perimeter of the rectangle in terms of x and show that this rectangle cannot have a perimeter of 12 cm. the perimeter of the rectangle in terms of x is __ cm