Let Cheetah speed be c, let Zebra speed be z
Cheetah speed is (=) 61 miles per hour less than 3 * zebra running speed.
c = 3z - 61.
c = 68 miles/hour
c = 3z - 61
68 = 3z - 61
3z - 61 = 68
3z = 68 + 61
3z = 129
z = 129/3
z = 43
Zebra speed is 43 miles per hour