Question 1094790
Let c be # of child tickets sold
Let a be # of adult tickets sold

a=4c (eq. 1)
1271.20=5.80c+9.90a (eq. 2)
sub eq. 1 into eq. 2, since a=4c
1271.20=5.80c+9.90(4c)
1271.20=5.80c+39.60c
1271.20=45.40c
1271.20/45.40=c
c=28

Therefore, 28 child tickets were sold that day.