Answer:
children = $6 ; adults = $13 
Explanation:
6c + 8a = 140
12c + 9a = 189
3c + 4a = 70
4c + 3a = 63
3c = 70 - 4a 
c = 70/3 - 4/3 a 
4(70/3 - 4/3 a) + 3a = 63 
280/3 - 16/3 a + 3a = 63 
(-16a + 9a)/3 = 63 - 280/3 
-7/3 a = (189 -280)/3 
-7/3 a = -91/3 
a = - 91/3 · -3/7
a = 91/7 
a = $13
c = 70/3 - 4/3 · 13 
c = 70/3 - 52/3
c = (70-52)/3 
c = 18/3 
c = $6