For this case, the first thing you should do is define variables:
 x = number of balls that contains the square.
 On the one hand, we have:
 left side: square + 6 balls
 On the other hand:
 right side: 10 balls
 We then have to balance:
 x + 6 = 10
 Clearing x we have:
 x = 10-6
 x = 4
 Answer:
 a linear equation that represents the model is:
 4) x + 6 = 10; x = 4
