Respuesta :

soccer ball = a = 5
basketball = b = 9
volleyball = c = 7

a + b + c = 21
2a + c = 17
2b + c = 25
2a + b + c = 26

Seeing that....
a + b + c = 21
2a + b + c = 26
We can deduce that a = 5

2a + c = 17
2(5) + c = 17
10 + c = 17
Subtract 10 from both sides
c = 7

2a + b + c = 26
2(5) + b + 7 = 26
10 + b + 7 = 26
17 + b = 26
Subtract 17 from both sides
b = 9

Hope this helped!
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