Why is this 21 on AMC 12?Algebra Level 3
Cozy the cat and Dash the dog are going up a staircase that has s stairs. Cozy the cat goes up two stairs at a time and Dash the dog goes up five stairs at a time. At the end, both of them will take a smaller leap to get to the top if necessary. Dash has jumped 19 times less than Cozy. Find the sum of the possible values of s.