Find the sum of 1+1/3+1/6+1/10+1/15+1/21upto 20 terms

Alaptop computer is purchased for $1350 . after each year, the resale value decreases by 30% . what will the resale value be after 5 years?

What is the value of x in the following equation? -3x-2=2x+8

Afarmer has a large field that is x feet in length. he wants to fence in a rectangular section in the middle of the field , leaving a length of 100 feet of open field behind each end of the fenced rectangle. he also wants the width of the fenced-in space to be 100 feet less than its length. find the expressions to represent the length and width of the fenced section of the field