If we pretend that eachpairof pulls isonepull then we have a common difference of and a first term of . If we were to pick each term it'd be harder to establish a common difference making it harder to solve.

Since we're treating each 2 pulls as 1 pull then we can treat pulls as pull we can treat this as the sum of an arithmetic sequence (total distance=sum in this case) using the standard sum formula, subbing in your values of and you should get the answer required