Let's call:
J: number of cards that Jasper has
E: number of cards that Ethan has
Jasper has 6 more cards than Ethan:
J = E + 6 (eq. 1)
Two times Ethans plus 3 times Jaspers is 68:
2E + 3J = 68 (eq. 2)
Replacing equation 1 into equation 2:
2E + 3(E + 6) = 68
2E + 3E + 3*6 = 68
5E = 68 - 18
E = 50/5
E = 10
From equation 1:
J = 10 + 6 = 16