Answer:
Kari = 20 hours
Chris = 10
Mark = 10
Explanation:
K is Kari's hours
C is Chris's hours
Karis = 2 x C = K
Chris = C
Mark = C
3C - 10 = K
Assume C is 10 (since 10 is 1/3 of the hours mentioned)
2 x 10 = 20 so K worked 20 hours
20 is twice as much as 10 (C's hours)
and it's 30 - 10 (10 less than 3 times as many hours as Mark)
