is this geometry for enjoyment and challenge? i have this textbook too!!
to find the distance between the two points, use the distance formula, which is the sqrt((x1-x2)^2+(y1-y2)^2). so you would have sqrt((6+10)^2+(8-0)^2). so you have sqrt(16^2+8^2), which is the sqrt(256+64). that's sqrt(320) as your answer, which is abt 17.89