The position of an object moving along a line is given by the function s(t) = -7t^2 +70t. Find the average velocity of the object over the following intervals.
(a)​ [1,5]
​(b) ​[1,4​]
​(c)​ [1,3​]
​(d) ​[1, 1​+h] where h > 0 is any real number.