If n represent a number, then write an expression for three times the difference of the number and six increased by four times the number

Average acceleration: i have no idea how to do this.

How to do this , and can some one explain

Miss henderson wants to build a fence around a rectangular garden in her backyard in the scale drawing the perimeter of the garden is 14 in of the actual length of a b is 20 ft how many feet of fencing what you need