Can someone me find the area of this triangle

What is the common difference in the following arithmetic sequence? 7,3,-1,-5

Figure abcde is a regular pentagon. segment ae is located at a (2, 1) and e (4, 1). what is the perimeter of abcde? 4 units 6 units 8 units 10 units

Which simplifys to a+ b? a-(1-b)+1 -(1-a)-b+1 (a--1) -1)+1